This happened to me too. In my case, it was specifically after being hooked and pulled by one of those large aberrant elites. Instead of stopping in front of him, I was yanked off the map completely and fell down to a checkerboard surface where I was unable to move. Please look into this, thanks!

I had similar happen in one of the core end levels in act 1 where I was able to spacebar roll off the edge of the map and land in an area that was all black with a bluish beam of light on top of me. I could TP back to town but then had to wp and walk all the way back to where I was. They need to hire testers to find collision bugs like this wherever they are so they can be fixed.