Have you tried a reboot of both your router and the Sonos speaker? Or deleting the favorite, and setting up a new favorite? Or reauthorizing your Spotify account in the Sonos controller?

I would also recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it, or post the diagnostic number here for a Community Moderator to pick up.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the phone folks, there are more options available beyond just the diagnostic analysis.