Given that this is happening in UNA CMS involving the Messenger module and comment tables, probably the simplest and safest fix is to:

• Identify which bx_*_cmts table(s) have the “wrong” collation.
• Use ALTER TABLE to set them to the same collations as the others.
• Clear any cache in the UNA Studio / Dashboard after making database schema changes.

⚠️ Before making any modifications, always create a full database backup.

mysqldump -u USERNAME -pPASSWORD DATABASE_NAME > backup.sql

Here are a few ways to fix or work around this issue:

Align Collations / Character Sets

Login into MySQL

mysql -u USERNAME -pPASSWORD DATABASE_NAME 

Check the character set and collation of all comment tables (bx_*_cmts):

SHOW FULL COLUMNS FROM bx_table_name; 

If they differ, alter the tables so they use the same character set and collation:

ALTER TABLE bx_table_name MODIFY column_name VARCHAR(…) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci; 

Make sure the main text columns used in the UNION operation match exactly.