Hi Ritual Ground, it seems very likely this is linked to the other reports of thralls taking fall damage - see links below to a couple of threads on the topic - one of which you yourself ‘passed to the team’
(and that’s just the one’s I could find from a search - from memory, we’ve seen several other threads and bug reports on this topic since the update to ch4).
It seems that somehow Fall Damage has been switched on for thralls - this would mean that any player using an elevator would risk their follower impersonating a lemming and dying.