Soo... I was taming a horse. I put some diamond horse armor on it.
What I expected to happen was...:
I thought it would just tame the horse, and it did.
What actually happened was...:
I got the "Complete Catalog" advancement. When I put the diamond horse armor on it, the horse was invisible.
Steps to Reproduce:
1. Tame a horse. You get glitch A.
2. Put diamond horse armor on it. You get glitch B.
3. Aaand then you have an invisible horse and a random advancement. Good job!
Related issues
duplicates
Attachments
Comments

Thank you for your report!
However, this issue is a Duplicate of MC-137563 and MC-138541.
If you have additional information, please add it to that report.
Please search before reporting, as it's likely that one exists already.
Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Customer Support – 📖 Game Wiki

Small side-note: It also happens with gold and iron horse armor.