So, I've basicaly read every single thread that talks about it, and yeah, it's simply "unkown".
The most advanced theory was a limit on the number of blessings/banes to 6. However late game I'm often around 7 blessing and the godlike computer with boosts often reaches 8.

If you have a solution, please share.

My own theory was something about the number of magi (players+IA), since I got this only in the Planes conquest style thing. It also fit the number of active players. However I don't see how an IA could revive itself from death to overflow the limit.

(Edit : forgot to add that, "perhaps" the games consider Neutrals and Monsters as being "sort of factions", which maybe cause weird stuff if they capture special buildings. Although I've killed of whole empires without issues, it could have to do with the act of building)

Next I tried all kinds of back loading turns before, but no kuddos. The IA seems determined to crash the game.

Next I tried to mess with some diplomacy : since it's the IA doing something on their own turn, what if I mess with the diplomacy status to "convince" it to do something else. Didn't work.

Although I haven't been able to check, I've been wondring if this has to do with a limit of temples/holy grounds. Since I always play maximum (players, size, dificulty), I've seen the Ren mod litters holy grounds everywhere, so I guess more people would complain ?

My last resort was to analyze the message, but I'm basicaly noob at coding. To put it simply, if we could identify what that "itemsize=41", with a list of possible things it could be, maybe we could identify the ones with a 6 limit.

Well, as a conclusion, I'll just add the advice someone put there : play with 1 less IA magi, and this seems to reduce the problem from happening...

Now I'm gonna cry for my hundreds of wasted turns. T_T