Entities randomly despawn in large numbers when logging in and out of the game. This includes villagers, passive mobs I have bred, villagers (nametagged and traded with), hopper mine carts, paintings, armor stand with armor and items, nametagged hostile mobs (ravagers specifically), nametagged skeleton horses, bees, and tamed wolves and cats. All entities have been confined to single chunks and are unable to cross chunk borders. It seems to happen during updates, when the game crashes, or other instances of logging out without using the “save and continue” option.