This started happening before the last patch. No idea how to reproduce, but I see players with this bug every few games.
https://streamable.com/yn3nb
Players falling through world
Indeed this happens when one of the player's animations just completely fails. They usually just stand in 1 place, but then their character would move around without the animation. Usually when they start to rig a cache with explosive, they fall through the ground and in some other occasions. Probably crouching and stuff like that.