Animals and Villagers are disappearing

I’ve been seeing a lot of mobs disappearing in my friends realm, my horses, donkeys, cows, sheeps, pigs, and villagers keep disappearing for months now. I even named my villagers so that way I can keep track of them and more than half of them disappear every now and than. My village is walled up and lit so I know mobs can’t get in or spawn. Now my pets like foxes and cats are disappearing since the realm keeps reverting to the most recent save file.