Answer:
Go to your account overview and head to the Offline Devices section, then click 'Remove All Devices'. As a heads-up, you'll need to re-sync your tracks, but it should resolve the issue.
If that doesn't help, try a clean reinstall of the app, log back in, and try downloading some music for offline listening!
Didn't help? Search for more Spotify Answers, or create a new thread and ask the Community.
