Reset Glitch

Help, every time my friend logs into our multiplayer world, his whole inventory is reset and he is placed back at spawn with a starter map. This only happens to one of my friends, the other two and I are having no issues. I play on Windows 10, and some of my friends play on Xbox One. The friend that is having this "player reset glitch" plays on Nintendo Switch. how can he fix this? he's lost lots of stuff