On my Java world whenever I spawn in I have the same inventory. If I place a block 10 blocks away, get out of the world. When I get back in the block is back in my hand but 10 blocks away from me is the same block that I placed. It doesn't save changes to my inventory or cords but it does save the world changes. I think this might be my fault because I did 2 things. It was in hardcore, when I died I opened to LAN world and changed my game mode back. I then changed the world back to not LAN. I also used NBTExplorer to go to the world files, go to Level.Dat, go to Hardcore. Changed it from 1 to 2. Then it was in survival not Hardcore. I have a build I don't wanna lose but I'm not to far into the game. So if I cant fix it I guess I will just have to make another. I don't know what the "Affects version/s" means but my world is on version 1.16.5 and I'm on Windows.