Game goes out of sync as host?
I was playing the last level as WarMage with a Shotgun on Nightmare with my friend and at some point towards the end (3rd or 2nd last wave) my grenades stopped firing where my reticule was pointing, instead it kind of rolled them to the lower right of me along the ground and at the same time both my Secondary and Primary attacks stopped hurting enemies. Had to use my Fear and Stun All abilities to give my friend time to come over and finish 'em off for me. It fixed it self when the wave had finished being dealt with.
I also often notice that the shrapnel effect from my my Shotgun when performing Primary Attack often doesn't appear. I just get the spark/sun flair effect with no debris emitting from it.
I am the one that hosts (Invites my friend) so I shouldn't go out of sync I would've thought.