Based on the error code, I was thinking it was like this issue Upgrade gone sideways [deprecated Guest Gate plugin], which made me concentrate on getting the plugins up-to-date. However, there may also have been an issue where they’d manually forced the old PSQL, and they fixed that before cleaning up the old plugins (which then fixed things properly) Upgrade gone sideways [deprecated Guest Gate plugin] - #3 by dylanb
But I’m afraid resolving that is beyond my skill level. Does that topic give any extra clues for you?