Simply put, if you kill an enemy while they are attacking or doing a dash attack at you (Knight in Crucible) the moment they are mid animation, then an invisible wall pops up on death where the animation would have stopped.
This also occurs after the death of the (Guy with a weird Caged head and cage-like weapon) where when they die and you are far enough away from them it will create an invisible barrier around them that takes 1-2 seconds to disappear.
I’ve noticed other streamers who had issues with permanent Invisible walls after killing enemies on stairs which caused them not to progress to further areas.