I downloaded the latest snapshot of Minecraft, entered my world to see the new features, but there was something that caught my eye. I realized that my zombie horse was "invisible". I checked to see if it had some effect, but it didn't have any, so what could've caused this. I tried testing the selectors at the zombie horse, but it says "no entity found" even if I typed zombie_horse. I tried summoning it. It worked but it said "Summoned new Zombie" and it's still invisible. I middle-clicked it, and it gave me a zombie spawn egg instead of the zombie horse spawn egg.