Hey, I know this is a very late update, but I had the same issue which I believe is caused by Potala Palace. I am on v15.5.1 with VP v3.10.14 and a few other mods (details in the attached Lua Log below).
The World Congress has been founded in my case, but the CTD happens anyway.
Edit: I can also provide the save file and any other logs if they'll help you figure out the issue.
Edit2: I have confirmed that it is indeed Potala Palace that causes it. If I change the production to something else, the game continues as normal, and only crashes the moment Potala Palace is supposed to be completed at the start of the next turn.
(I don't know if it's some weird interaction with Community Events - as the Potala Palace wonder looks for a city state active event. I'll try another game or two without it in 4.x with v15.6x and the rest of the mods being similar and I'll keep you updated if the bug reappears.)