During my experience playing within the new Snapshot, I happened to get off of my horse for a moment and the horse took (if it had about 8 hearts) 6 hearts. And another horse was completely killed and all I did was stand above a layer of glass in the middle of the night and it was immediately when I got off, it wasn't attacked.

I also had moments where I was trying to move up and down grass (1 block up) and it had to be precise to walk across it without my horse's head having a weirdly aggressive up and down shake, as if it was trying to go up, but couldn't.

To be clear, it can go up 1 block terrain, it just randomly struggles unless i walk onto a straight path rather than in prior versions it working just fine.