Overall: villagers despawning. Every time I log in, one of my 5 villages has maximum level villagers despawning. Villagers are kept in safe, well lit areas, some despawning even being in 2x2x2 houses made of glow stone with a bed, workstation and iron door opened with levers. The most recent time one village of 10 armorer villagers (in a 20x10x3 extremely well lit single building) was down to 2 overnight.