I confirm that if you close/shutdown Sync before shutting down the computer, Sync does not open in a window on the restart. It would appear that this is the source of the issue and perhaps the requirement to adjust the program before the release of the latest version of Windows was missed. By the way, I have the same issue with Skype for Business (similarly, it won't open in a window if you close/shutdown Skype for Business before shutting down the computer).