I went to my horse pen and my horse was invisible. I can ride it and access the inventory. I remove the saddle and she remains invisible. I remove the Iron Horse Armor and she becomes visible. I tested it with other armors and those also turn her invisible. She is a Sooty Black horse if that has anything to do with it. I only have one horse.

What I expected to happen was...:
The horse to appear wearing the Horse Armor

What actually happened was...:
The horse becomes invisible while wearing Horse Armor

Steps to Reproduce:
1. Put Horse Armor on tame horse