The real issue is probably MariaDB 10.4 and Strict Mode.
We know that phpVMS 5.5.2 will work under MariaDB 10.1 . Some users have reported issues with MariaDB 10.2 and above. Some of these issues were related to Strict Mode. Search here for "strict mode".
Your work-around may work. There may be other DB tables that may need the same adjustments. Only time will tell. Keep us advised in this thread if you notice other similar issues.