Noticed this mostly on realms. I am owner of the realm. I play daily. I had a secured village, rather tall wall, no openings, and approximately 15 villagers and an iron Gollum. I log off properly. I log on next day and the village is down to 3 villagers and no Gollum. I repopulate the village to over 15 villagers ( I have beds for 20+) and make 2 Gollums. I log off properly. I come back the next day to 3 villagers and no gollums. No signs of attack. No villager zombies and wall is intact. I also had about 30 adult chickens in a fenced area. They are down to 2 adults and 5 chicks. Others have reported same thing on minecraft forum.