mysql show processlist hanging processes;
If the users were migrated by adding records to the mysql.user table, rather than by issuing GRANT statements, then you need to... 

mysql&gt; FLUSH PRIVILEGES;


...so that these new records will be read and used by the server.

(Yes, "flush" sounds like "delete" but it's not -- in MySQL, it's more like "close and re-open.")

The two threads you posted are not hung, they're idle.  Your "backup server" appears to be (or have been) a replica/slave server.  The first thread one is the replication IO_thread that reads events from the master, and the second one is the replication SQL_thread, that executes those events.  The second one looks normal; the first one is attempting to re-connect to the master server, which, I gather from your question, may now be offline.

They aren't affecting the inability to log in, but if you really want them to go away... this should do it...

mysql&gt; STOP SLAVE;