When my sister joins my world, sometimes her full data resets. She gets a starting map and everything.

When my sister joins her world data sometimes resets. It happened today, and she spawned in the End, with a starting map, as if the world spawn was in the End and she just joined for the first time. It happened one other time, and I exited the world and went back in and she got her stuff back, so hopefully that happens this time, but I hope this bug gets addressed soon. Thank you.