Aye I get this alot and I for the most part coop with the other half, its either her or me looting that makes the game pause, also had it a lot when Im jumping in and at the same time she is dropping a aoe like witchfire. I put the later down to my PC being a bit old but the loot thing is an odd one.

Yep, that is exactly what happens to me, either a loot chest, a large drop or before someone speaks - the game will pause for half a second or so.  It’s annoying as hell, but I like the game so I put up with it.  Hopefully there will a fix before long.  Possibly just before the console release.