This is a known bug that is affecting MySQL only. It is caused by the GROUP BY clients.client_id on line 24 of the clients.php
We have no fix in sight for this for MySQL users and are trying to reach out for additional help to anyone that may have a fix.
The problem is if we remove the GROUP BY clause it creates duplicate clients and sometime more depending on how many tags are assigned to the client.
We highly recommend against using MySQL and instead use MariaDB as we test thoroughly with MariaDB.
To get it working for your instance you will have to remove line 24 all together, and on each update until a fix comes out.
If you have any SQL skills you can try playing around with the the query on lines 12 through 26 of clients.php file and see what you come up with.
In the meantime we are focusing on some other higher backend priorities that need major attention within the code.