The error report in your rgl.log isn’t very informative. If you are certain the crash is clan related, I suggest you go through all the governor changed entries in your rgl and mark those towns/castles off vs your settlements.xml to determine which towns/castles haven’t been given an initial governor. IDK what order the game works through them but that may become obvious. One of those unprocessed towns/castles must be next in line after Château de Quélennec. So, I’d assume that the clan assigned to own that next town/castle might be the one causing your crash. If so, that might narrow the focus to resolve the problem.
If not, I suggest you go back to basics and check all the steps required to create custom kingdoms from a guide
https://www.nexusmods.com/mountandblade2bannerlord/mods/3185
Alright I did some testing.
In two different crashes, the 10 last governor assignments were identical. It assigned from vlandia clan 1 all the way to clan 5. The order in which governors were assigned seemed to be based on family status, from old to young. So usually the first governor was the clan ruler's spouse, and then oldest child and so on. Unless there was another lord in the clan that isn't direct family but older than the ruler's wife. Regardless, it never reached clan 6. Clan 6 happens to be one of only 2 with the special character 'â' in the name, so I replaced it with a normal 'a'. The next try it seemed to work, it loaded that clan's governors (although suddenly favoring the rulers wife instead of older non family member lord, so now I'm unsure of the actual order the governors are chosen) and a couple other houses after but still crashed.
This time though it crashed before reaching battania clan 7, which has no special characters in its name nor in any of the clan members' names. I let the game crash again to check the crash log, and to my surprise it again failed to reach the same governor assignment as it did the first two times so removing the 'â' seemed to not do anything anyway.
Now I'm not so sure what is still causing the crash. I double checked the related clans' entries in the xml, the settlements, the lords of the clans and everything is correct, no misspellings or anything although I don't think the game would even launch properly if there were.