I have a survival world I sometimes play with my brother. We've made a lot of progress, including beating the dragon, getting elytra, and defeating the wither. Today when I joined, I found myself at the default world spawn, with nothing in my inventory but an empty map. Upon reaching my base and looking in my ender chest, I found that all the data for my profile on the world was gone. I had lost many valuable items, such as wither skulls, a fully enchanted netherite sword and pickaxe, an enchanted elytra, and lots of other assorted valuables. I have no idea what caused this to happen, but it needs to be fixed immediately.