I've noticed that when I'm playing coop, there are several circumstances that cause the game to freeze and crash while I'm saving (I'm the host).
1) My partner logs out while the save is in progress.
2) My partner is involved in dialogue or a menu while the save is in progress.
I suppose in both of these situations my partner may have performed these actions just before I hit save. In the first situation, I was able to see that a player disconnected while the save was taking place.
