I do have a multi-server setup too.
The usename 'ispconfig' might be confusing compared to a ispcsrv* one, as it was set manually during the trancission from a single to multiserver setup in the past.
Is there still something in the sql statement besides the user, that indicates to you that this is not a multi-server setup?
If I understand correctly
UPDATE `mysql`.`tables_priv` SET `Timestamp` = NOW( ) , `Table_priv` = 'Select,Insert,Delete' WHERE `tables_priv`.`Host` = 'SERVERNAME' AND `tables_priv`.`Db` = 'dbispconfig' AND `tables_priv`.`User` = 'USER' AND `tables_priv`.`Table_name` = 'monitor_data' LIMIT 1 ;
Where SEVERNAME and USER are replaced with the correct values of course
should fix it for me?