Entities consistently disappear over time. Passive mobs in my world slowly disappear. Not all mobs in my world are affected, although it's few that do not disappear. Minecart hoppers always disappear but regular mine carts do not. Almost all my villagers eventually disappear but have two or three that do not (kept in the same space). It seems almost as if passive mobs that have exsisted the longest are the only ones that don't disappear any new mobs I add to farm or my base etc eventually are gone. It isn't all at once it's slowly over time, one here a few there. Does not happen after nether visits, is not mobs escaping enclosures. Quiet frustrating to create large complex (iron farms, villager breeders sheep/cow redstone farm etc) builds that depend on mobs to operate just to have them despawn. Oddly villagers in my trading area kept in minecart out of village range (64+ blocks) do not despawn (so possibly something wrong with villages?) My world is on realms, survival switch between mostly peaceful and easy sometimes (doesn't happen after switching).