Spotify when are you going to get it togther on the donwloaded tracks on playlists. Trying to keep up with all those that are randomly erased from my device, sometimes all tracks I have, is a BIG pain in the **bleep**. I'm no tech but I bet if you give me a week in your shop I could figure out a fix. Just do it please!
Updated on 2018-11-27
You should keep an eye on the 'Offline devices' listed in your account settings. The same device may be added several times which may make your offline downloads to reset. Delete any duplicate or unrecognized devices you may see.