The attacked image can’t show the troll itself since we moved on past it hoping it would despawn, but we got stuck at the drop towards the final stretch just before the boss. I took the image in the stairwell on the way up just before the host closed the game because it was bugged.
The troll was hit by Flame Wiz’s dash and got stuck inside the wall, it was constantly moving in place halfway inside the wall at a diagonal position down a narrow corridor near a drop. No damage could be done to the troll for whatever reason.
Looking at the amount of health, perhaps it got stuck just as it was between going in and out of its invulnerable few seconds before you hit it while it’s down or as it’s getting up.