There’s a lot to take-in in your post, however can you first clarify which Countries you have in use for your Amazon, Spotify and Sonos profiles? 

Could you post a screenshot of your 4 Sonos devices in your Alexa App device list please

Could you also login to your Amazon account online and goto ‘manage content and devices’ area and take a screenshot of your Sonos devices that are on the Devices Tab inside ‘other Alexa devices’ - (see screenshot attached).

Also can you tell me what you can see at the ‘login with Amazon’ link - the below is an example URL to see that information, but it points to the U.K. Amazon site you may need to alter it to your own countries Amazon site.

https://www.amazon.co.uk/ap/adam?_encoding=UTF8&ref_=ya_mb_login_with_amazon

Can you see anything there that relates to Sonos and/or Alexa.

Lets begin with those things first of all.. I just want to see if there is anything obvious you might have missed.

In addition to the recommended steps from @Ken_Griffiths . An Alexa device showing as offline is caused by it's inability to connect online. As the Sonos Move is battery powered as well as mains, can you confirm that you powered down the device by taking it of it's base and then holding the power button for 10 secs, at the back of the device. Leave the device for 30 secs then press and hold the power button until the device powers back on. After 1 min, check that the device is shown as online.

Sorry about the long post. I wanted to make sure I mentioned every step I took as I had done a lot of things to try and fix the issue.

I have set the following countries for my services:

• Amazon: US account
• Spotify: Denmark account
• Sonos: Currently set to US (I change it to US, then add Alexa to my capable Sonos speakers, then change back to Denmark. This worked without any issues before. Now whilst troubleshooting I’ve kept the account set to US)

Attached you will find:

• My 4 Sonos devices in the Alexa app
• Other devices on my Amazon account
• Active Apps on Amazon

I am not sure why there are 6 devices listed under Other devices. The Sonos One is the Kitchen and the Sonos Move is the Bedroom. They seem to be appearing twice on the Amazon website. There are only 4 in the Alexa app.

Using the login with Amazon link I see Sonos with Alexa voice services.

Shortly after I started this topic, I went back onto the Alexa website on desktop and tried several times to enable the Sonos skill. Suddenly the skill was enabled. I could then ask Alexa to play music and she would play from every speaker. Peace was restored for a brief time.

The following day from the morning until perhaps late afternoon, Alexa worked with Sonos. Until suddenly it didn’t. She would say that she would play the requested song without anything happening. After asking her again she then told me “Sorry, that device is offline”.

I cannot figure out what has changed in my setup as it used to work perfectly fine until this week.

The devices are never shown as offline in the Alexa app or Alexa website. I did try taking the Move off the base and powering it off by holding the power button for 10 seconds and then leave the device for 30 seconds. I then turned it on and popped back online. Still wouldn’t play music when asked.

The reason there are 6 devices on the Amazon website is the Kitchen Sonos One has an Alexa component - think of it as a separate device which is called ‘Kevin’s Sonos One’ and it’s the same thing too for your Bedroom Move, it’s Alexa component is called ‘Kevin’s Sonos Move’.

You can see the two Alexa components in the Amazon App device list, by selecting either your Bedroom or/and Kitchen speaker and going to it’s properties (just click to open) - please just check the components are there. (Let me know if they are missing).

This next bit isn’t important and not relevant to your issue, but I would respectfully suggest renaming Lounge 2 to something different - Alexa is likely to get confused with the similarly named ‘Lounge’ speaker and I also recommend you don’t name your Alexa Group the same name as any of your devices for similar reasons.

Moving on..

I don’t see an issue with your Amazon App, or the Alexa information online.. it looks good to me. I think this is all to do with your Country settings. I think your Spotify Country profile settings may need to be the same as your Amazon Country profile settings, so I would try changing that back to what you had before. So start with that first of all and also when done remove and reinstall Spotify in your Alexa App and also your Sonos Controller App.

Then try again and see if that works for you.

I would also perhaps go onto try playing a radio station from tunein on your Sonos devices using Alexa, just to see if that works, as that too may indicate that all is well between Sonos and the Alexa Assistant. It also would mean we then need to concentrate on why Spotify isn’t ‘playing ball’.

It maybe the case that Spotify, or Amazon, are clamping down on their users using other Country settings to bypass things, but let’s just see how you get on with changing the Countries back to what you had previously and reinstalling the Spotify service to both Alexa and Sonos,

Thanks for the clarification on the Alexa components.

If I click Bedroom in the Alexa app it will show me the ‘Kevin’s Sonos Move’ as the only thing. Is that intended? Same thing with Kitchen but with ‘Kevin’s Sonos One’:

I have renamed Lounge 2 per your suggestion to something completely different.

My Spotify country has always been Denmark but before I consider changing that I would like to let you know about my recent experience:

Today, when I woke up, I asked Alexa (Sonos Move, Bedroom) to play music. And music played! Fabulous. I then asked her to stop after a few minutes and she stopped. I asked her to “Play music on Bedroom” to which she replied “Sorry, that device is offline”. I asked her to “Play music” and she said the same thing.

I tried TuneIn as well and that does not seem to work either. I’ve asked her to:

• “Play BBC Radio 2”
• “Play BBC Radio 2 in Kitchen”
• “Play BBC Radio 2 in Bedroom”

She will say that she will play the radio in question from TuneIn but then nothing plays.

If I access the Alexa app and set it to play TuneIn on any named Sonos speaker (Bedroom, Kitchen, Lounge, Perch (former Lounge 2)), nothing happens. If I select Kevin’s Sonos Move or Kevin’s Sonos One she will say that “BBC Radio 2 from TuneIn isn’t available right now”. If I select my Echo Dot the radio will play.

It would seem it’s not just Spotify but TuneIn as well. I’m guessing that means it’s the connection between Alexa and Sonos specifically that’s not doing so good..

Here’s a list of devices that I’ve attempted to play TuneIn on in the Alexa app:

Yes, your components ‘Kevin’s Sonos Move’ and Kevin’s Sonos One’ are correct and are intended.
 

To get the BBC Radio Stations working you may need to also install the BBC Sounds ‘Skill’ in the Alexa App. 
 

In the Amazon Alexa App, do you have any Amazon Groups or ‘other’ Smart-home devices called ‘Bedroom’ besides your Move in the App..if so can you remove those temporarily and try again.

Can you also kindly clarify if your Amazon Account is still set to U.S. or have you put it back to Denmark?

I had this issue a while ago,  probably a couple of years. 
so this may not work but may be worth a try. The issue back then was that you had to use the website NOT the app on your mobile. Remove and reinstall the Sonos speaker via the Alexa website and so if that helps. 

I only have one group called “All” where everything is grouped together. That’s how it has been for years and has worked for me until recently.

My Amazon Account is still set to US.

Regarding the skill “BBC Sounds”, I can’t find that one. However, I just tried to ask Alexa Echo Dot to “Play BBC Radio 2” and she played “BBC Radio 2 from TuneIn” on all my Sonos speakers. I then asked her to stop and play a specific song and she played it on all speakers.

So why did that work all of a sudden? I hadn’t changed a thing.

The song ended and I asked her to “Play ABBA in Kitchen”. She said “This is ABBA from Spotify playing on Kitchen”. No music was playing though. I asked her again and she replied the same thing. I tried with Bedroom as well. She says she’ll play but nothing plays. No mention of things being offline though. Simply asking her to “Play music” does nothing other than her saying she’ll play but then nothing plays.

Could my router be affecting the whole setup? I haven’t noticed any issues with WiFi with my other devices in general (Sonos will play fine through its own app, smartphone seems to be doing fine, Alexa is able to play on herself through the Alexa app and computers seem fine too) but I reckon I should consider every option considering how its going so far..

Thanks for the suggestion. I’ve tried that a handful of times with no success :(

Do you know how long it would take for Alexa to be able to use the reinstalled speakers? Did it work for you immediately or did it take a while?

Yes, sometimes Sonos ‘ghost’ speakers can still get listed in Alexa itself, albeit none are presently showing in the online account through ‘My content and devices’

A user can go onto open this website (You may have to open this website on a PC) alexa.amazon.com goto -> Smarthome -> Devices -> scroll down to ‘remove all’ button. 

Then use the Sonos App to setup Alexa again on each speaker, but perhaps go that route when everything else has been tried. I’m still thinking it might still perhaps be a ‘Country’ settings issue. 

I have seen talk on this forum in the distant past that some Services were considering using the card payment ‘address’ stored within an account to confirm Country settings - so it’s possible that something may have changed with Spotify or Amazon perhaps? 
 

NOTE: it’s worth checking that the latest Amazon, Spotify & Sonos Apps are installed on the mobile controller device too. 

I’m also going to suggest that each of the speakers and the router are also rebooted.