Villagers keep despawning

My villagers keep despawning. I log onto minnecraft after not being on for one day and all my villagers just vanished randomly. This has happened to me many times. My villagers are safely living in a house I made for them with and iron golem that also disappeared. They all have name tags and I see no possible way they could have died from mobs as the doors are iron doors and the iron golem is supposed to protect them. This is an extremely frustrating issue that needs to be fixed.