PineappleTyrant

This has happened for me in the past few versions of minecraft also, however I have only just started to loose progress from it

I had this exact same issue. I found a llama, dragged it through an extreme hills biome to get all the way home, only for me to realise it was gone after I had left and returned to my world 2 times as I was working on a building project and therefore wasn't paying much attention to my llama.

My llama was named and was wearing a carpet, and was in a fenced area which it couldn't have escaped.

I have this exact issue as well. It also effects grass growing on grass blocks for me though.