I think Spotify decides what to show in the app. Maybe you could ask them too?
The titles show in the Sonos app. It’s when I hit the “play” button that the error occurs.
I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it.
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, they have tools at their disposal that will allow them to give you advice specific to your Sonos system and network.
This will cover the Sonos’ ability to reach Spotify’s servers. If the issue turns out to be as @106rallye suggests, on Spotify’s part, there will be a limited amount that Sonos folk can do.