I would never approve a production system as expansive as Gitlab's to only have two databases in a cluster. That is asking for trouble, and any {sys,db}admin worth their salt will tell you the same. As soon as you need to do anything on one database, you've just lost your cluster policy.
The lack of automation, especially around validating db backups, failover (not having the failover process scripted and tested is _begging_ to have a nightmare at 2am where you're reading documentation on how to fail over a db), etc.
The simple thing of having your hostname / $PS1 say the machine's purpose could have stopped this. All prod machines have a bright red PS1 and a clear name of <type>-<service>-<prod/dev/etc>-<region>-<dc>.corpnet in my setups.
All of this is reflected in their discussion style, meeting style, etc. Ad-hoc, not very carefully designed, random off-hand comments. Obviously a young team with a lot to learn. Nothing wrong with that, but a lot of customers are relying on their skills! Learn quick!