Added it as a radio station, when I listen to it, I hear the music 1 second , 1 second silence, 1 second music, 1 second silence etc etc.
Maybe you can try to stream songs to Sonos for offline playback. Sono supports to add music from the local music library. The upper limit numbers of tracks are 65,000, which sometimes might be less, depending on how large of the track’s metadata. But I think it is enough. Then you can stream local songs to Sonos music library to avoid this error happens.
The next step is to download Spotify as into the local music library. It is unavoidable to use a third-party tool, AudFree Spotify playlist converter to unlock the protection in Spotify songs. Just convert your favourite track to mp3 then add it to Sonos.
When you play music on your phone, you need to establish the connection between the music app and Sonos, then the music will be started on Sonos. Or you could download music and then play them which may be more stable. For example, you could directly download Spotify music or download Spotify music to MP3 via Spotify music converter. Then you could listen to Spotify music on Sono even offline.