I’ve decided to just not bother with the Slaughter arenas at all any more since more than half the time for me they become unable to complete because some enemy has either wound up way off-map or gotten stuck in a spawn container. They cant be seen or affected by any weapon or ability so the mission fails because youbhave no choice but to quit to the menu.
This has happened to me often enough on story missions (Ive finished TVHM with all 4 characters) where you have to clear an area to proceed which, albeit annoying, isnt a big deal since you just continue on after reloading. But it renders slaughter arenas pretty pointless when the glitch forces you to start over from scratch. I just had it happen 4 times in a row in the Cistern, each on different rounds and at different points on the map. Why even bother?