My latest adventures were with 5.30.1; I’ve been running into this (these?) problems since 2.24.1. I narrowed it down the 5.22.0 as the first occurrence, so the MM devs have created a ticket to look into the changes between 5.21 and 5.22.
I’m setting up a new server with up-to-date PostgreSQL and up-to-date Mattermost and it’s running fine. Magic!