It’s not clear what the actual problem is here, will Spotify not play at all, or is the audio playing and you are getting audio interruptions?

Is it the same via both the Spotify App and the Sonos App spotify service? 

Have you tried any of the Spotify troubleshooting steps, such as ‘logging out’ of all devices via their online services in your account settings?

Although other music services are working okay, you could also perhaps try reducing any potential opportunities for local interference by changing your routers 2.4ghz WiFi channel-width to 20MHz and perhaps changing the WiFi channel itself - its best to use a fixed ‘non-overlapping’ channel, either 1, 6 of 11 and if using the internal SonosNet connection (with one Sonos device wired to the LAN), then also ensure it’s channel in the Sonos App network settings is set so that it is at least 5 channels away from your chosen router channel.

There are other things you can maybe try later, but I would perhaps start with those few steps to hopefully assist stronger network connections and to avoid the potential for intermittent wireless interruptions. 

I’d also be tempted to just a reboot of the router followed by the Sonos speakers, on the offhand chance that they are  holding on a bad DNS address for the server Spotify uses to feed Sonos, which is a different one than Spotify uses to feed their own app. 

To clarify:
Sonos will not play Spotify at all. Music does not even begin to play. Spotify will play from a Roku, cell phone and desktop app.

As originally stated, everything has been rebooted and every item in the system was reset to default.

I did change the 2.4GHz control channel to 11 and that did get things playing using the Sonos desktop app but this is confusing and doesn’t make sense since local libraries would play as well as other services (SoundCloud) would play prior to this as was stated in the OP. Though I do have a theory why this may be the case.

After updating the channel I also experienced problems with the Spotify Connect feature. If the Sonos app has a queue it will play those songs instead of what was being played from the Spotify app. If there is no queue the song progresses but there is no sound.

Additional diagnostic: 619527224

So just to clarify, Spotify works from the desktop App, but it won’t work/play at all from the mobile controller.
 

Also Spotify ‘connect’ will not work from the mobile controller. Have you got another mobile, or tablet with the App installed that you can quickly try, as it sounds very much like the issue is related to the mobile communicating over its WiFi connection with your Sonos speakers. 
 

Have you tried rebooting your mobile device and recreating it’s WiFi network connection to your router.

Note, If you are using an iPhone or iPad, there is a feature in the iOS network connection settings called ‘Private Address’ (it’s a MAC spoofing feature) you could also try toggling off that feature to see if it solves things.

I see you mentioned you are using channel 11 for your WiFi connection…if you do have any Sonos products wired to your network, then can you check your SonosNet channel in the Sonos App ‘Settings/System/Network’ is not set to channel 11. It ideally needs to be set to either channel 1 or 6. 
 

If you have any Sonos products near to your router, or any other wireless access point, can you try moving them, so that they are at least one metre away from those network AP’s to reduce any potential for interference.

Presently with the router controlling the 2.4GHz band on channel 11 the Sonos app (mobile and desktop) will play Spotify from it’s interface.

Spotify Connect (from within the Spotify interface) will not play if the queue is empty in the Sonos app. If there is something in the Sonos app then it will play that and not what is being called to play in the Spotify app.

SonosNet is channel 6 (didn’t need wired connection to see that). But that is still strange why it only causes issues with Spotify. Are it’s API’s slower/worse than SoundClouds or Sonos when using local libraries? Does it run interference/signal strength checks before playing and have a lower tolerance?
 

Hi @funkygrandmother 

Welcome to the Sonos Community!

Neither of the diagnostics you sent came through successfully - I recommend you get in touch with our technical support team, who will go through some real-time troubleshooting with you.

Having said that, rebooting the router by turning it off for at least 30 seconds may help.