Confirming that I am also having the same issues with cats in Java Edition 1.15
It's annoying that we now have to sign into X box live to go on servers. I, and probably many other kids, now have the issue of their gamer tag that they use on servers being claimed by some guy who has claimed the tag and dose not use it anymore, resulting in a loss in claimed plots, homes set, your inventory and possibly your reputation. I'm just hoping this new feature gets removed in the next update. And before you ask why I didn't just not update until I had got round this, the server had already updated.
I had the same problem. Villager who was caged in vanished. At one point I saw green sparkles like he was there, then later he popped out of a wall. But then after a night he vanished and never returned.