Characters Disappearing/Auto Deleted

I’m curious what is going on. I’ve made a post awhile ago about this to get no response other than asking if the char wasn’t expired/perm.

No it wasn’t expired
Yes it was perm’d
It was a mule with full inv/stash
I didn’t play it for about 1 week
It just vanished

Before 1 week afk while I still had char, I was crafting a diadem with a few hundred skulls I traded for. the other mules holding skulls are still there along with my main character.

I’ve asked around on bnet and forums and saw there are quite a few other people this has happened to, too. Glitches happen, I understand that. What can I do to try to prevent this in the future?

edit: same thing to someone else: