game crashing

Been playing in team with my friend and 3time out of 4 when we try to do some maps, the game crash when we hit the portal. When we manage to get through and clear the map, the game crash on the return portal. If one of us die and the other one keep going for a little while or clear the map, the game also crash on the return portal and we both get to the login screen. Eatch time we have a crash we're send back at the login screen.