I have the same problem and wasted alot of time trying to fix it. I now have installed an older version and all is working like it shoult be Although the older version is running slower i rather have the spotify connect feature.
Older version doesn't work for me. I can connect, hit the play button, then while to music does start playing on my Sonos, the Spotify Connect shows the Play button again, as if it stopped playing and the connection is lost. All this while the Sonos continues to play.
Reauthorized the account on Sonos, same faulty behavior described above.
I guess only reverting does not completely fix the issue.
Re: Can't connect to Sonos players in Spotify Connect
This FINALLY was the solution for me. Worked 100%. Makes sense too as it was a few weeks back that i got the latest update to spotify and thats when i stopped being able to play on my sonos speakers from the spotify app. I just deleted the Spotify app, downloaded this older version via the link above, and low and behold works fine......Then i went into the Play store, searched for the spotify app there and made sure to turn off auto updates......I dont want to grab the latest version again and break this feature once again.