So I included a save (attached files) right before I take Bucarest (and the game crashes), the situation is as follows:
Russia captured Bucarest, and took precious oil that I needed back, so I move forces there. When doing so I don't capture tiles for myself but for an allied city state instead, meaning most tiles around Bucarest are not mine, but my allies', maybe this has something to do with it.
I couldn't find debug logs which is referred to in other threads, if they are needed let me know.
Russia captured Bucarest, and took precious oil that I needed back, so I move forces there. When doing so I don't capture tiles for myself but for an allied city state instead, meaning most tiles around Bucarest are not mine, but my allies', maybe this has something to do with it.
I couldn't find debug logs which is referred to in other threads, if they are needed let me know.