An AI has been engaging in a battle for more than 150 turn against one of those "free city" (the grey people I don't remember how they're called). I don't when they started this battle, I discovered this part of the map after it started. Since then, this battlefield is constantly on, which makes me unable to get access to my second uranium and third petrol sources. I'm not sure what cause this bug but I remember getting something similar in a beta. I started to besiege the city of an AI and we peace out before I started attacking. It can be a different issue though as here the AI was attacking/sieging a "free city".