donkey goes invisable when dismounted

Put the summary of the bug you're having here

What I expected to happen was...:

The donkey to be normal

What actually happened was...:

The donkey was invisible and not mountable, making it so I have to exit the world and load the world again

Steps to Reproduce:
1. get a donkey, my donkey had a saddle and a chest
2. get off the donkey
3. sometimes disappears