Henrique A

 Also happened to my villagers in multiple occasions. My trading hall is over 10 solid blocks underground, with no sky access anywhere around 50+ blocks, and they constantly turn into witches. I had to enable cheats in my world and disable the weather cycle. Found this youtube evidence as well: https://m.youtube.com/watch?v=jEAfxLnaiic

Very sorry to open this duplicate. I hate to do that. I did search for it though and couldn't find 😞

I'm also having this issue. The custom skin show as pure black when selecting it. And then it just switches beck to Alex.