Cannot GRANT privileges as root
Oh my goodness, I think the problem stems from mixing the mysql schema of different mysql versions. First of all, run this query:
desc mysql.user;

For MySQL 8.0, you get 51 columns
mysql&gt; desc mysql.user;





Field
Type
Null
Key
Default
Extra




Host
char(255)
NO
PRI




User
char(32)
NO
PRI




Select_priv
enum('N','Y')
NO

N



Insert_priv
enum('N','Y')
NO

N



Update_priv
enum('N','Y')
NO

N



Delete_priv
enum('N','Y')
NO

N



Create_priv
enum('N','Y')
NO

N



Drop_priv
enum('N','Y')
NO

N



Reload_priv
enum('N','Y')
NO

N



Shutdown_priv
enum('N','Y')
NO

N



Process_priv
enum('N','Y')
NO

N



File_priv
enum('N','Y')
NO

N



Grant_priv
enum('N','Y')
NO

N



References_priv
enum('N','Y')
NO

N



Index_priv
enum('N','Y')
NO

N



Alter_priv
enum('N','Y')
NO

N



Show_db_priv
enum('N','Y')
NO

N



Super_priv
enum('N','Y')
NO

N



Create_tmp_table_priv
enum('N','Y')
NO

N



Lock_tables_priv
enum('N','Y')
NO

N



Execute_priv
enum('N','Y')
NO

N



Repl_slave_priv
enum('N','Y')
NO

N



Repl_client_priv
enum('N','Y')
NO

N



Create_view_priv
enum('N','Y')
NO

N



Show_view_priv
enum('N','Y')
NO

N



Create_routine_priv
enum('N','Y')
NO

N



Alter_routine_priv
enum('N','Y')
NO

N



Create_user_priv
enum('N','Y')
NO

N



Event_priv
enum('N','Y')
NO

N



Trigger_priv
enum('N','Y')
NO

N



Create_tablespace_priv
enum('N','Y')
NO

N



ssl_type
enum('','ANY','X509','SPECIFIED')
NO





ssl_cipher
blob
NO

NULL



x509_issuer
blob
NO

NULL



x509_subject
blob
NO

NULL



max_questions
int unsigned
NO

0



max_updates
int unsigned
NO

0



max_connections
int unsigned
NO

0



max_user_connections
int unsigned
NO

0



plugin
char(64)
NO

caching_sha2_password



authentication_string
text
YES

NULL



password_expired
enum('N','Y')
NO

N



password_last_changed
timestamp
YES

NULL



password_lifetime
smallint unsigned
YES

NULL



account_locked
enum('N','Y')
NO

N



Create_role_priv
enum('N','Y')
NO

N



Drop_role_priv
enum('N','Y')
NO

N



Password_reuse_history
smallint unsigned
YES

NULL



Password_reuse_time
smallint unsigned
YES

NULL



Password_require_current
enum('N','Y')
YES

NULL



User_attributes
json
YES

NULL





51 rows in set (0.00 sec)
For MySQL 5.6, you get 43 columns
mysql&gt; desc mysql.user;
+------------------------+-----------------------------------+------+-----+---------+-------+
| Field                  | Type                              | Null | Key | Default | Extra |
+------------------------+-----------------------------------+------+-----+---------+-------+
| Host                   | char(60)                          | NO   | PRI |         |       |
| User                   | char(16)                          | NO   | PRI |         |       |
| Password               | char(41)                          | NO   |     |         |       |
| Select_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Insert_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Update_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Delete_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Create_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Drop_priv              | enum('N','Y')                     | NO   |     | N       |       |
| Reload_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Shutdown_priv          | enum('N','Y')                     | NO   |     | N       |       |
| Process_priv           | enum('N','Y')                     | NO   |     | N       |       |
| File_priv              | enum('N','Y')                     | NO   |     | N       |       |
| Grant_priv             | enum('N','Y')                     | NO   |     | N       |       |
| References_priv        | enum('N','Y')                     | NO   |     | N       |       |
| Index_priv             | enum('N','Y')                     | NO   |     | N       |       |
| Alter_priv             | enum('N','Y')                     | NO   |     | N       |       |
| Show_db_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Super_priv             | enum('N','Y')                     | NO   |     | N       |       |
| Create_tmp_table_priv  | enum('N','Y')                     | NO   |     | N       |       |
| Lock_tables_priv       | enum('N','Y')                     | NO   |     | N       |       |
| Execute_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Repl_slave_priv        | enum('N','Y')                     | NO   |     | N       |       |
| Repl_client_priv       | enum('N','Y')                     | NO   |     | N       |       |
| Create_view_priv       | enum('N','Y')                     | NO   |     | N       |       |
| Show_view_priv         | enum('N','Y')                     | NO   |     | N       |       |
| Create_routine_priv    | enum('N','Y')                     | NO   |     | N       |       |
| Alter_routine_priv     | enum('N','Y')                     | NO   |     | N       |       |
| Create_user_priv       | enum('N','Y')                     | NO   |     | N       |       |
| Event_priv             | enum('N','Y')                     | NO   |     | N       |       |
| Trigger_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Create_tablespace_priv | enum('N','Y')                     | NO   |     | N       |       |
| ssl_type               | enum('','ANY','X509','SPECIFIED') | NO   |     |         |       |
| ssl_cipher             | blob                              | NO   |     | NULL    |       |
| x509_issuer            | blob                              | NO   |     | NULL    |       |
| x509_subject           | blob                              | NO   |     | NULL    |       |
| max_questions          | int(11) unsigned                  | NO   |     | 0       |       |
| max_updates            | int(11) unsigned                  | NO   |     | 0       |       |
| max_connections        | int(11) unsigned                  | NO   |     | 0       |       |
| max_user_connections   | int(11) unsigned                  | NO   |     | 0       |       |
| plugin                 | char(64)                          | YES  |     |         |       |
| authentication_string  | text                              | YES  |     | NULL    |       |
| password_expired       | enum('N','Y')                     | NO   |     | N       |       |
+------------------------+-----------------------------------+------+-----+---------+-------+
43 rows in set (0.15 sec)

For MySQL 5.5, you get 42 columns
mysql&gt; desc mysql.user;
+------------------------+-----------------------------------+------+-----+---------+-------+
| Field                  | Type                              | Null | Key | Default | Extra |
+------------------------+-----------------------------------+------+-----+---------+-------+
| Host                   | char(60)                          | NO   | PRI |         |       |
| User                   | char(16)                          | NO   | PRI |         |       |
| Password               | char(41)                          | NO   |     |         |       |
| Select_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Insert_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Update_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Delete_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Create_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Drop_priv              | enum('N','Y')                     | NO   |     | N       |       |
| Reload_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Shutdown_priv          | enum('N','Y')                     | NO   |     | N       |       |
| Process_priv           | enum('N','Y')                     | NO   |     | N       |       |
| File_priv              | enum('N','Y')                     | NO   |     | N       |       |
| Grant_priv             | enum('N','Y')                     | NO   |     | N       |       |
| References_priv        | enum('N','Y')                     | NO   |     | N       |       |
| Index_priv             | enum('N','Y')                     | NO   |     | N       |       |
| Alter_priv             | enum('N','Y')                     | NO   |     | N       |       |
| Show_db_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Super_priv             | enum('N','Y')                     | NO   |     | N       |       |
| Create_tmp_table_priv  | enum('N','Y')                     | NO   |     | N       |       |
| Lock_tables_priv       | enum('N','Y')                     | NO   |     | N       |       |
| Execute_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Repl_slave_priv        | enum('N','Y')                     | NO   |     | N       |       |
| Repl_client_priv       | enum('N','Y')                     | NO   |     | N       |       |
| Create_view_priv       | enum('N','Y')                     | NO   |     | N       |       |
| Show_view_priv         | enum('N','Y')                     | NO   |     | N       |       |
| Create_routine_priv    | enum('N','Y')                     | NO   |     | N       |       |
| Alter_routine_priv     | enum('N','Y')                     | NO   |     | N       |       |
| Create_user_priv       | enum('N','Y')                     | NO   |     | N       |       |
| Event_priv             | enum('N','Y')                     | NO   |     | N       |       |
| Trigger_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Create_tablespace_priv | enum('N','Y')                     | NO   |     | N       |       |
| ssl_type               | enum('','ANY','X509','SPECIFIED') | NO   |     |         |       |
| ssl_cipher             | blob                              | NO   |     | NULL    |       |
| x509_issuer            | blob                              | NO   |     | NULL    |       |
| x509_subject           | blob                              | NO   |     | NULL    |       |
| max_questions          | int(11) unsigned                  | NO   |     | 0       |       |
| max_updates            | int(11) unsigned                  | NO   |     | 0       |       |
| max_connections        | int(11) unsigned                  | NO   |     | 0       |       |
| max_user_connections   | int(11) unsigned                  | NO   |     | 0       |       |
| plugin                 | char(64)                          | YES  |     |         |       |
| authentication_string  | text                              | YES  |     | NULL    |       |
+------------------------+-----------------------------------+------+-----+---------+-------+
42 rows in set (0.01 sec)

mysql&gt;

For MySQL 5.1, you get 39 columns
mysql&gt; desc mysql.user;
+-----------------------+-----------------------------------+------+-----+---------+-------+
| Field                 | Type                              | Null | Key | Default | Extra |
+-----------------------+-----------------------------------+------+-----+---------+-------+
| Host                  | char(60)                          | NO   | PRI |         |       |
| User                  | char(16)                          | NO   | PRI |         |       |
| Password              | char(41)                          | NO   |     |         |       |
| Select_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Insert_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Update_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Delete_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Create_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Drop_priv             | enum('N','Y')                     | NO   |     | N       |       |
| Reload_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Shutdown_priv         | enum('N','Y')                     | NO   |     | N       |       |
| Process_priv          | enum('N','Y')                     | NO   |     | N       |       |
| File_priv             | enum('N','Y')                     | NO   |     | N       |       |
| Grant_priv            | enum('N','Y')                     | NO   |     | N       |       |
| References_priv       | enum('N','Y')                     | NO   |     | N       |       |
| Index_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Alter_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Show_db_priv          | enum('N','Y')                     | NO   |     | N       |       |
| Super_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Create_tmp_table_priv | enum('N','Y')                     | NO   |     | N       |       |
| Lock_tables_priv      | enum('N','Y')                     | NO   |     | N       |       |
| Execute_priv          | enum('N','Y')                     | NO   |     | N       |       |
| Repl_slave_priv       | enum('N','Y')                     | NO   |     | N       |       |
| Repl_client_priv      | enum('N','Y')                     | NO   |     | N       |       |
| Create_view_priv      | enum('N','Y')                     | NO   |     | N       |       |
| Show_view_priv        | enum('N','Y')                     | NO   |     | N       |       |
| Create_routine_priv   | enum('N','Y')                     | NO   |     | N       |       |
| Alter_routine_priv    | enum('N','Y')                     | NO   |     | N       |       |
| Create_user_priv      | enum('N','Y')                     | NO   |     | N       |       |
| Event_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Trigger_priv          | enum('N','Y')                     | NO   |     | N       |       |
| ssl_type              | enum('','ANY','X509','SPECIFIED') | NO   |     |         |       |
| ssl_cipher            | blob                              | NO   |     | NULL    |       |
| x509_issuer           | blob                              | NO   |     | NULL    |       |
| x509_subject          | blob                              | NO   |     | NULL    |       |
| max_questions         | int(11) unsigned                  | NO   |     | 0       |       |
| max_updates           | int(11) unsigned                  | NO   |     | 0       |       |
| max_connections       | int(11) unsigned                  | NO   |     | 0       |       |
| max_user_connections  | int(11) unsigned                  | NO   |     | 0       |       |
+-----------------------+-----------------------------------+------+-----+---------+-------+
39 rows in set (0.00 sec)

mysql&gt;

For MySQL 5.0, you get 37 columns
mysql&gt; desc mysql.user;
+-----------------------+-----------------------------------+------+-----+---------+-------+
| Field                 | Type                              | Null | Key | Default | Extra |
+-----------------------+-----------------------------------+------+-----+---------+-------+
| Host                  | char(60)                          | NO   | PRI |         |       |
| User                  | char(16)                          | NO   | PRI |         |       |
| Password              | char(41)                          | NO   |     |         |       |
| Select_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Insert_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Update_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Delete_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Create_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Drop_priv             | enum('N','Y')                     | NO   |     | N       |       |
| Reload_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Shutdown_priv         | enum('N','Y')                     | NO   |     | N       |       |
| Process_priv          | enum('N','Y')                     | NO   |     | N       |       |
| File_priv             | enum('N','Y')                     | NO   |     | N       |       |
| Grant_priv            | enum('N','Y')                     | NO   |     | N       |       |
| References_priv       | enum('N','Y')                     | NO   |     | N       |       |
| Index_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Alter_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Show_db_priv          | enum('N','Y')                     | NO   |     | N       |       |
| Super_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Create_tmp_table_priv | enum('N','Y')                     | NO   |     | N       |       |
| Lock_tables_priv      | enum('N','Y')                     | NO   |     | N       |       |
| Execute_priv          | enum('N','Y')                     | NO   |     | N       |       |
| Repl_slave_priv       | enum('N','Y')                     | NO   |     | N       |       |
| Repl_client_priv      | enum('N','Y')                     | NO   |     | N       |       |
| Create_view_priv      | enum('N','Y')                     | NO   |     | N       |       |
| Show_view_priv        | enum('N','Y')                     | NO   |     | N       |       |
| Create_routine_priv   | enum('N','Y')                     | NO   |     | N       |       |
| Alter_routine_priv    | enum('N','Y')                     | NO   |     | N       |       |
| Create_user_priv      | enum('N','Y')                     | NO   |     | N       |       |
| ssl_type              | enum('','ANY','X509','SPECIFIED') | NO   |     |         |       |
| ssl_cipher            | blob                              | NO   |     | NULL    |       |
| x509_issuer           | blob                              | NO   |     | NULL    |       |
| x509_subject          | blob                              | NO   |     | NULL    |       |
| max_questions         | int(11) unsigned                  | NO   |     | 0       |       |
| max_updates           | int(11) unsigned                  | NO   |     | 0       |       |
| max_connections       | int(11) unsigned                  | NO   |     | 0       |       |
| max_user_connections  | int(11) unsigned                  | NO   |     | 0       |       |
+-----------------------+-----------------------------------+------+-----+---------+-------+
37 rows in set (0.01 sec)

mysql&gt;

For MySQL 4.x, you get 31 columns
mysql&gt; desc mysql.user;
+-----------------------+-----------------------------------+------+-----+---------+-------+
| Field                 | Type                              | Null | Key | Default | Extra |
+-----------------------+-----------------------------------+------+-----+---------+-------+
| Host                  | varchar(60) binary                |      | PRI |         |       |
| User                  | varchar(16) binary                |      | PRI |         |       |
| Password              | varchar(16) binary                |      |     |         |       |
| Select_priv           | enum('N','Y')                     |      |     | N       |       |
| Insert_priv           | enum('N','Y')                     |      |     | N       |       |
| Update_priv           | enum('N','Y')                     |      |     | N       |       |
| Delete_priv           | enum('N','Y')                     |      |     | N       |       |
| Create_priv           | enum('N','Y')                     |      |     | N       |       |
| Drop_priv             | enum('N','Y')                     |      |     | N       |       |
| Reload_priv           | enum('N','Y')                     |      |     | N       |       |
| Shutdown_priv         | enum('N','Y')                     |      |     | N       |       |
| Process_priv          | enum('N','Y')                     |      |     | N       |       |
| File_priv             | enum('N','Y')                     |      |     | N       |       |
| Grant_priv            | enum('N','Y')                     |      |     | N       |       |
| References_priv       | enum('N','Y')                     |      |     | N       |       |
| Index_priv            | enum('N','Y')                     |      |     | N       |       |
| Alter_priv            | enum('N','Y')                     |      |     | N       |       |
| Show_db_priv          | enum('N','Y')                     |      |     | N       |       |
| Super_priv            | enum('N','Y')                     |      |     | N       |       |
| Create_tmp_table_priv | enum('N','Y')                     |      |     | N       |       |
| Lock_tables_priv      | enum('N','Y')                     |      |     | N       |       |
| Execute_priv          | enum('N','Y')                     |      |     | N       |       |
| Repl_slave_priv       | enum('N','Y')                     |      |     | N       |       |
| Repl_client_priv      | enum('N','Y')                     |      |     | N       |       |
| ssl_type              | enum('','ANY','X509','SPECIFIED') |      |     |         |       |
| ssl_cipher            | blob                              |      |     |         |       |
| x509_issuer           | blob                              |      |     |         |       |
| x509_subject          | blob                              |      |     |         |       |
| max_questions         | int(11) unsigned                  |      |     | 0       |       |
| max_updates           | int(11) unsigned                  |      |     | 0       |       |
| max_connections       | int(11) unsigned                  |      |     | 0       |       |
+-----------------------+-----------------------------------+------+-----+---------+-------+
31 rows in set (0.01 sec)

Picture this scenario:

You install 5.0
You uninstall 5.0
You forgot to move /var/lib/mysql out of the way
You install 5.1

The user permissions start getting shifted. Whenever you run SHOW GRANTS;, it is hardwired to expect columns in specfic places in mysql.user (given the fact that mysql.user is a MyISAM and its ROW_FORMAT is Dynamic (Default)). It is very easy to see a user suddenly lose permissions when you reload a MySQL 5.0 version of mysql.user into a MySQL 5.1 instance.
In the future, should you ever decide to reload users into MySQL, try to dump the users to a text file using pt-show-grants rather than mysqldump.
I actually wrote my own version of pt-show-grants as follows:
mysql -hhostaddr -umyuserid -pmypassword --skip-column-names -A -e&quot;SELECT CONCAT('SHOW GRANTS FOR ''',user,'''@''',host,''';') FROM mysql.user WHERE user&lt;&gt;''&quot; | mysql -hhostaddr -umyuserid -pmypassword --skip-column-names -A | sed 's/$/;/g' &gt; MySQLUserGrants.sql

This will produce all user grants as SQL, which is far more portable than standard mysql techniques. Simply reload the SQL script and the GRANTS are executed. Of course, such reloading is only forward compatible, never backward.