Hey, ran into this issue with a game save,

My friends Jamie and I had a world he was hoasting. he had to go, and i wanted to keep playing, so i saved a copy of the world. He happened to be looking at the belt layer while i saved it. so when i loaded it back up, he was standing in the world. (but just as a generic player) while I was playing (alone) bugs killed his player and when he rejoined to play with me, the game crashed and said the world was corrupt.

I can't recreate this issue to provide a log ATM due to a lack of a 2nd player
Im not worried about recovering the world either