Villagers keep despawning

My villagers keep despawning, even with a name tag.

They take there doors from there houses with them (not always)

There are no hostile mobs around (got a lot of torches around)

I have to level all new villagers to the point they where.... this is getting really annoying to do

 

Hope you know a fix for this.

 

P.S.

Why does it say: versions: Version with id 'Java 1.15.2' does not exist. ??

My launcher and in game it says Java edition 1.15.2....