Villagers and Named Pets Despawn

Villagers will despawn.

Villagers housed in large pen, with no dark patches & iron golems for extra measure. Woke up one day and they had all vanished. 

After finding new villagers and moving them to the self-made village, this happened again after a few days. Villagers had been traded with, and the second time the iron golems vanished too. 

Named wolf also disappeared from my base.