Fell through the floor, Zalmarath fight.

https://imgur.com/gallery/floor-n1EZXMC

Rolled Southwest, on the west side of map (around the top of the cracks).

I was rolling away from the drones he spawns and was pushed over the side and fell below. Leaving my character alone kept me there for about 10 seconds before I clicked and was brought back up. Specifically, the same location I fell, top of the crack, left side.