Chunks unload, allowing for people to fall out of the world

On all consoles, chunks will unload, allowing people to fall out of the world, In the overworld I might add, and lose all their items and a horse. I have attached a file of one of my friends Spawn unloading, trapping him in an infinite loop of death. After restarting the server, all items in chests are fine, but his horse is gone, and the items he had in his inventory are gone. This also happened earlier today where the same thing happened.