Insert and Update with AES_ENCRYPT is mangling character set on double byte script DB and fields are UTF8_unicode_ci collation - MySql v 5.6

HTML charset is utf 8

Double byte script was entered successfully prior to this issue (Chinese, Japanese, plus Cyrillic etc) when using plain non encrypted input.

But trying to use AES_ENCRYPT on input mangles all non-english script.
DB field is BLOB.

 UPDATE mytable SET bodytext=AES_ENCRYPT('任車心是，防少劇和的；子反華不就','aeskey') WHERE t_id=123


produces strings of question marks - English is fine though

I'm not sure if I should try to CONVERT the input to UTF8 first - but when I try that I get an error.
Any suggestions of what to review?
Forcing utf8mb4 does the trick. Run a query against MySQL immediately after making the connection with:  

SET NAMES'utf8mb4';

Alternatively, use these settings in your my.cnf file to get the same effect:

[client]
default-character-set = utf8mb4

[mysql]
default-character-set = utf8mb4

[mysqld]
character-set-client-handshake = FALSE
character-set-server = utf8mb4
collation-server = utf8mb4_unicode_ci


(Note: These settings are defaults (for the most part) in MySQL 8.0 and MariaDB 10.3, so this probably isn't a problem there.)

Chinese (and other) scripts are multibyte - standard utf8 allows 3 bytes per character - fine for plain text but using AES_ENCRYPT ON 3 bytes requires another byte - thus setting utf8mb4 allows the required 4 bytes per character.