My Animals And Villagers Keep Despawning

All of my animals and villagers keep despawning. I had an entire village going on (secure, well lit, with golems) and all but one of them (golems included) are gone. 

Additionally, my animals keep despawning. I had a pen with cows, sheep, pigs, and llamas, but all except for a few llamas and one cow have somehow disappeared. Help?