My Game Keeps crashing while I am in a Party with my one Friend

I have had 3 crash's so far since I started grouping up with my friend.  It happen mainly 2 times when loading in or starting the beginning of game. Even To both of use at the sometime and once when I crashed and my friend stayed in the game. I don't have any of these problems happening when solo playing but grouping up is become a big problem. Note: I play on PC and my Freind is playing Playstation