Not to be contradictory (but I am going to be), this is a good indication of some sort of temporary network interruption between your Sonos speaker and your router.
I’d start by a full network refresh, by unplugging your Sonos devices from power, then rebooting your router. Give the router a couple of minutes to reload everything properly, then plug back in your Sonos speakers. This will cause the Sonos devices not only to get new IP addresses, but also reload the Sonos firmware that runs them. Wait another couple of minutes for Sonos to settle in, then test.
It is less likely, based on your post, but still possible that your system is suffering from some sort of wifi interference , which might be worth double checking.
I just tried starting a Spotifyplaylist from within Sonosapp (instead of Spotifyapp) and it won’t have this issue, so to me it really looks like Spotify/Sonos integration issue.
Great, I’m glad you’ve determined the issue. You may want to report it to Spotify, who operates the server that Sonos points to.