My player gets deleted when I rejoin the world.

It started with my brother occasionally getting his stuff deleted and completely restarting in our online worlds and I thought it was just his profile. But then my other brother started getting the same problem as well as their skins changing when they join. I still didn't report it until today when the same thing happened to me and I can't fix it this time. Because before we could reload the game and it would go back tomorrow but now I only have what was in my chests and lost a lot of progress. Please people vote this to be fixed because it is completely ruining the game.