I use Spotify Premium both on my Android and Windows.
For at least past 6 months I'm unable to download my playlists at Windows app. When I toggle "download" it works fine, but when Windows restarts it resets and all playlists get back to Online mode. Android works fine.
I'm sure other people has/had the same issue, but couldn't find the solution on my research.
I've waited 6 months hoping for an update that could fix that. No lucky.