possibly its one of the reasons I hate the 0 gait creatures. they can't personally move from off to on the map in migration moves. Personally such creatures need to be designed as say [DOES NOT EXIST]? maybe and then only possible through dfhacking into the fort from reactions to keep them from being stuck on the outskirts.
I have no idea if it actually would be causing the crash in question. Misaligned body parts, usually doesn't cause a crash, DF is designed to handle that, and generally I've only seen that appear with the random generated creatures... Which is why I usually don't turn them on, and they should be off by default in 1.29.