I'm still playing on the version 2.7.2 and the latest corresponding CK2+, as the Archon of a merchant republic, and I have reached a point where I am consistently getting crashes on a very specific date 2 days after the autosave. (The last things I remember doing were going out to gather ingredients, specifically herbs, as a Hermetic initiate, and starting to write a paper, plus I also got the event where I was in seclusion and my daughter begged to go out for the night, only to bring back a peasant boy she wanted to marry.) I checked all four beta changelogs and no found "crash fixes" that I might recognize as responsible for the issue. Would it be worthwhile to upload the save so you can take a look at it, or is there just no chance you'll be able to do something with the save?
On a related note, patrician gameplay has a couple other issues. I got several random crashes during the game (while having, as far as I can remember, zero crashes in my Yngling game, the other game I played to any great length on this version), so I suspect that there may be a merchant republic event that's doing something wrong and crashing the game. (The previous crashes were not reproducible on a specific date though, so maybe not? I dunno.)
Also - I do not seem to be able to call my Court Physician to sick relatives while being a patrician (but not the head of the republic), despite having a physician (I checked).
Finally, I'm not sure if this is WAD or not, but when taking a loan as a patrician (again, while not heading the republic), repaying the loan has no negative financial consequences (unlike normal, when you'd get a tax malus to your counties). You merely have to pay 400 prestige (possibly scaling up with realm size?), compared to 100 prestige for promising to repay later. Just thought I'd mention this in case it wasn't the intended mechanic.