One of my Era 300s wont play with Spotify

Have you rebooted both speakers? Don’t Factory Reset without further consult.

Thanks for reply. 

By reboot, do you mean power of and on? I have powered off and on the offending speaker. Then disconnected it and reconnected it. This am didn’t solve the problem instantly but as I say, weirdly, it started working again yesterday (possibly due to something I did or maybe not, and after a period of more problems) but isn’t this morning. 
 

it is working through Sonos app direct (even when playing Spotify music) just not when I “Airplay or Bluetooth” off Spotify app. 

Try the following:

1. Check for Sonos and Spotify app updates. If that doesn't correct the issue continue to next steps
2. Un-plug all Sonos
3. Reboot your router
4. Delete the Sonos app from your device 
5. Delete the Spotify app from your device 
6. Make sure your device is up-to-date
7. Plug-in all Sonos and let them come back *
8. Re-install the Sonos app and select “Join an existing system”
9. Sign-in to Sonos with your credentials
10. Reinstall Spotify app and sign-in with your credentials 
11. Test your Sonos and Spotify

 * The LED on the speakers should show solid white assuming you have LED status turned on in the app. If not wait 15 minutes after plugging-in the last speaker.

Hi. Thanks for the reply. Yes all three speakers show solid white LED. That is a right old rigmarole to go through though isn’t it? I can’t be doing this once a month…

is this a common fault, do you know?

So the 300s and Sub Mini are “Bonded” as a stereo pair + sub?  What is the name of the Room?  When you choose that Room in the Spotify app it only plays through one speaker?

I don’t expect this to be a frequent issue. When a pair is balky, rebooting (power) both is a good approach.

Yes they are bonded as a stereo pair. The name of the room is Living Room. And yes, when I choose that room on Spotify only one of the pair (plus the sub mini) plays. Interestingly, the non playing Era still controls the volume of the playing speakers if you use the buttons in the top. 
 

Also, for some reason, sometimes it just comes back to life and works fine (it did this evening, for example). 
 

And also weirdly, if I play through the Sonos app (not the Spotify app) it also works fine. 
 

It seems like there is something in the Spotify app that isn’t telling the left speaker to play, but the left is still connected to the right as it can control the right’s volume even if doesn’t play itself! 
 

Thanks for your help. 

Probably a silly idea, but can’t think of anything else.  Try unbonding the 300 stereo pair then make sure neither 300 has a name related to Living Room.  If either is related to the name Living Room change the name to something else.  Then rebond them as a stereo pair.  I told you it was silly.

Thanks MoPac. 
 

how do you mean “neither has a name related to living room”? They are not named as far as I know, but as a Sonos newbie I could be wrong. 

When you unbond them they will need to get named if they don't recall previous names.

I had issues with that name issue here.

Named them LS and RS and all was well.

I have exactly the same issue. When playing via Spotify one Sonos 300 of a Stereo Pair is playing intermittently while playing via Spotify. When playing via Sonos they both work fine.