Seriously...it barely works 40% of the time. A) I t can’t handle my full playlist, so I can’t listen to all my liked songs on random. 
Most of the time, it just says “connecting” for 3 or 4 minutes and then never connects. Rebooting phone, router, speakers...sometimes it works, sometimes it doesn’t.
Oh...and yeah, I’m running the latest versions of Sonos, Spotify, iOS, router firmware, etc.
Sonos wrote the API, but it is Spotify who did the integration of the API to the Spotify servers. Sonos doesn’t touch the stream until they play it on your speakers.
But it sounds more like you’re having local network issues. 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, there are more options available beyond just the diagnostic analysis.
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