I've had this issue too. All of my farm animals have despawned, including several mooshrooms which we had to bring all the way from a mushroom island around 20,000 blocks away. All my horses have despawned too, taking the saddles and armour with them.
Haven't noticed any items disappear from chests though.
This has recently started happening on my realm. Doors, chests, elytra, damage, dropping and picking items up and probably more all have fortnite sounds, potions look like slurp juices and make my game drop to a really low FPS on PC when someone is holding one and all of the paintings that I had changed in my texture pack are back to being default ones.