Max level Villagers with Name Tag keep despawning.

In a creative world of mine, I have an area with one villager in each profession. But for some reason, a few of the villagers keep despawning. The Villagers that keep despawning are maxed level and have a name tag applied to them. But still, they keep disappearing.

P.S. These villagers are in a confined area, and they can't leave the building.