My wife is first controller on Xbox series x and I am second controller we both have live accounts (no guest accounts). When we are playing in a splitscreen mode I am 2nd player. My inventory is gone and I start back at the first respawn area when we first began the game. This has been going on for weeks at a time every time we play I have to put all of my items on my character into a chest. I loose all my inventory and experience and basically start back as of I'm new to the world.  However my wife will have everything as she did when we saved and quit the game. It also resets my skin back to Steve.