This is the second time this has happened so I figured I should submit an issue report. So, twice now I've opened the game and it's asked to re-sign into my Microsoft account, and both times I would go the play my last played world only to find it not there. I have been able to get it back by finding the world folder and moving the level.dat file into a new folder, but the process takes a while, and even then it resulted in chunks of my world not loading correctly and the world spawn changed to a completely different part of the world.