Conspiracies. I think it's much more likely that your horse has developed some kind of AI (see 0:40 and further) and you refuse to share the secret with us On a more serious note: Haven't witnessed this so far myself, but it is not uncommon (in vanilla) for players to be invisible for a short while right after teleporting. Could that have been involved here by any chance?
I don't think so. When I was recording, I teleported to the spawn and back to my residence. There was no change. It's an interesting bug, though.
I've got that a couple times, both on emc and other servers. Logging out and back normally solves it.
Had the opposite happening, the horse was invisible so it looked like I was levitating just because I pressed a tp sign when I was riding it. It's funny tho it looks like your horse is alive.