During my numerous trips through Lower Karazhan mythic+ dungeons runs, I have always encountered some kind of bug where we pull mobs through the floor and it ruins the key.
When pulling the balcony before the first boss, DK tank uses blood boil and pulls Usher through the floor, which kills the healer and pulls Nazerim into the first boss fight.
When clearing trash mobs at Attumen, The Huntsman, and DK MC the horse, the horse stomp will pull trash from the floor above, which kills the healer and teleports to party and wipes key.
The horse stomp will pull Attumen if the stomp is cast within LoS of Attumen.
The dungeon feels full of bugs, and I hope you will fix this “pulling through floors” problem.