I'm rather amazed that after over 2 years this still seems to an issue. My desktop playlists and mobile playlists don't correspond...at all. It seems Spotify can't handle adding lots of music at once to a playlist, all is fine and dandy on the desktop app but somehow the mobile app does not sync the files equally. For example my favorites (starred) playlist has 0 tracks in while the mobile app show about 990, another playlist on the desktop has about 5700 while on the mobile app it's 2980.