I encountered similar issues with both the elk and sailboat a few days ago, where if the game crashes while you're riding on either they get stuck in some limbo state when you load back into the world. I dug through the audit logs to find the entity IDs and poked around with some of the debug commands to try to find them after this happens. From what I found the entities still exist in the world and seem to follow your character around if you search the location of the entity as if you're still riding them, but they're completely invisible and cannot be interacted with in any way. I haven't been able to find any way to pull them out of this state once this happens, so they're just kind of lost to the void.
