(Minecraft Bedrock) My villagers despawn, but they have name tags + doors?

My villagers despawn so often despite their name tags and lots of doors, but they are all in one room.

They can't actually despawn, no matter if it's a name tag or a door! It could be a bug, too, or just the zombies transforming them.

ps: also had that in bedrock today. Even with velcro horses.