Mule Disappearing EVERY DAY

EVERY day, when I log into the server there is about a 50/50 chance that my Mule will not be there.

 

My Mule is named, he has a saddle and a chest.

He is protected by being in the building with me, I can be looking at him AS I LOG OUT and half the time when I log back in after saving and quitting the game, he is just gone.

There is no damage to his pen, there are no other mobs near him.

I have to restore from a backup to bring him back. Some times I loose an hour of game progress because of this.

I can go to different parts of the world and consistently see other mobs (horses or donkeys) that I only mounted once to check their health and speed, but my trusted pet will just vanish.

MAKE IT STOP!!!!