Bottom line: Spotify seems to be blocking certain artists music from being streamed to music devices (in my case Denon Heos. I'm assuming this would probably would be the same for Sonos, but welcome someone to test?). Other music, sourced the exact same way streams fine (i.e. songs bought from iTunes, and added to Spotify local files and then playlists)
Workaround: I can stream Swift and Sting if I tell Spotify to stream to an Airplay device, rather than the Heos device directly. In my case this airplay device is connected to Heos via optical in.
Speculation: When you upload a track, Spotify checks certain details of the file, if they're not found in Spotify's database some kind of compliance check takes place, and a determination is made re: Can the user stream the song to another device or not. During this process you'll receive errors like "Can't play this right now". Later, once the validation is complete, that error will get replaced by "no error" and the song will just skip.
Examples: Sting Live in Berlin or Taylor Swift Wildest Dreams
1. Bought some songs from the iTunes store before I made the switch to Spotify (Drive - The Cars, Pet Shop Boys - Love comes quickly, Taylor Swift - Wildest Dreams, Sting - Live in Berlin Album)
2. Export songs to mp3 in iTunes
3. Add songs to Spotify local files
4. Drag songs from Local Files to spotify playlist
5. Wait for sync to iPhone
6. Play on iPhone (success)
7. Change target to a streaming device (Denon Heos) - works for PSB, The Cars, etc but not Sting or Taylor swift
- For Taylor Swift:
Initially: "Can't play right now"
Eventually: You hit play and it skips the track
- For Sting: multiple tracks
Initially: Can't play right now
Eventually: TBD - I'm betting it'll be the same as Taylor Swift tomorrow
1. Neither Taylor Swift nor Sting's Live in Berlin album are available on Spotify
2. Other music by Sting works fine