[Zubersoft]

It takes a very long time on Windows to delete all of the files due to the API used for accessing files in UWP applications. If you have a large library with several gigabytes of files, clearing them through the app may take a considerable amount of time. You'd be better off manually deleting the storage location files yourself (including the database file) as you can do that relatively quickly. Depending upon how long you were waiting, it's possible there was an error in MobileSheets, but you may just be used to how much faster it is in the Android version due to the ability to directly access files and delete them.

Mike