What I expected to happen was...:

Friend would join and reconnect with the correct playerdata.

What actually happened was...:

Friend joins but two versions connected, one is the 'original' containing previous inventory and in the location where they logged off. The 'other' is at worldspawn and has an Alex skin and an empty inventory. 'other' version is controllable by my friend and they report a ghosted version of the 'original' following. New playerdata file is made with a different UUID. Restarting both clients fixed the problem.

Steps to Reproduce: (not sure how to reproduce, these steps may not work, will update if able to find a method)

1. Create a world
2. Second player joins world, add things to inventory and move from world spawn
3. ?? Turn off internet, but not wifi
4. ?? Player duplicated