I think this is the solution:
1. Be sure to log out and shut down any instance of the standalone app running anywhere <--IMPORTANT
2. Log in via the web https://www.spotify.com/us/account/overview/
3. Choose "Offline Devices" from the left menu
4. Remove them all. I don't see any repercussions here. I guess it syncs afresh next time you use the app/login but doesn't matter really.
5. Change your password (also on the left menu)
I don't see any devices now and all my playlists are there and I am thinking that this won't happen again.
Incidentally, this is spotiamb. I don't even use Windows and have no recollection installing or trying it.