One more problem has appeared regarding Windows 10: It looks like the update will wipe all app data. In the case of music|mode, this means that all your playlists will be lost after the update, unless you manually export them before starting the update.
So if you plan to update to Windows 10 and you are using the playlists feature, please export them following these steps:
1. Select Playlist using right-click or tap-hold
2. Press „Save“
3. Select format and location
4. Repeat for all playlists
After the update, wait for the music library to update completely. Then open the „Playlists“ view, press the right mouse button (or swipe in from the bottom), press „Load“ and select the playlist file(s) you exported. The files will now be imported (which can take a while on large playlists).
I am really sorry for the users who have already lost their playlists. It is very unusual that a windows update just deletes app data of installed apps. This was not the case with previous updates, not even with major windows updates.