29-Jun-20 We will use this issue to track issues with missing Worlds on Xbox One in version 1.16 of Minecraft (Bedrock).
Please take time to allow your worlds to sync with the cloud fully. From our tests, it might take some time for large saves to sync correctly (20+ minutes), and you might encounter the message "your other console is taking to long to sync". Just press "Try again" (not sync current data) and it should eventually upload to the cloud.
It might take another 10+ minutes to download the world from the cloud, and at some time the progress bar might freeze for a couple of seconds but the transfer should complete.
Please note however, that we are not able to assist with the retrieval of worlds here at the bug tracker.
Account or syncing errors should be taken up with Xbox Customer Support directly.