I bought an Xbox One in early August 2015 and created a Minecraft file on the system. I was working on an interesting city and by October, it was coming along nicely. I decided to map out the surrounding world one day, but when I saved the game and tried to get back on the next day, my progress from the previous day was deleted. I figured that I had just forgotten to save or something, but when I got back on and played again, it still wouldn't save my progress (even when it said that it was saving). I created a new file, figuring that the previous one had been corrupted. After making decent progress on that new file since October, around November 20th, 2015, I had the same issue. Since then, I've tried everything to get it to save, but nothing works. I have turned autosave on and off, I've saved and then exited the game, I've exited the game without saving, I've copied the file and played on the duplicate, and the issue won't go away. In case you don't understand, this issue only occurs on files that have a lot of progress on them. Files with little or no progress are never affected. If you have a similar issue or may know a possible solution, please don't hesitate to comment!