After making some changes to the world, I exited to the menu and then locked the screen. Upon returning a few hours later to the world, all changes made in the last session were missing. I also notice this earlier in the day when I exited and went back in and I was not at the same place where I saved it, but rather where I saved it during the previous session.
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Duplicate of MCPE-1217, please use the search function to see if your bug has already been submitted. Currently over 50% of tickets are being closed as duplicate.