So I was just playing with my friend and we found a bug where you're unable to exit the reward screen you get after finishing some quests.
What happened is we had just finished a quest and were on the reward screen. My friend wanted one thing and I wanted another, instead of ending it in a civilised way he took over my character (that were the one who was receiving the reward) but I was still able to choose the reward and close the screen. This made it so my friend couldn't exit the reward screen and we ended up having to restart the game.
A few things that you'd maybe want to know; we were playing on the same computer in split-screen mode and my friend were the one who was the leader (the one that is able to save, I haven't tried this on any other quest yet but I suspect that that same thing would happen.