I would suggest perhaps trying the following:

1. Remove any/all instances of Spotify from your Sonos controller.
2. Reset your controller App by going to ‘Settings/App Preferences’ 
3. (Optional Step) goto Spotify online and sign out of Spotify on all devices.
4. Check and/or (if necessary) log into the native Spotify App on your mobile controller.
5. Open Sonos App and bypass the opening screens and agree to terms and select the option to connect to the ‘existing’ Sonos System - do not create a new system. Follow the onscreen instructions and sign into your Sonos Account.
6. Add the Spotify music service to your controller and sign into your Spotify account and assign the service with your chosen name to identify it as your account.
7. Goto your Wife’s mobile and open her Sonos controller App and now add your Wife’s Spotify account back to the system. Ideally this setups must be done from her mobile device and not your own mobile. On setup ensure to give the music service a different name so each separate linked Spotify service can be identified in the Sonos System and App.

Now see if the steps above have (hopefully) resolved your issue.

Thanks for the detailed reply @Ken_Griffiths . I will give this a try. 
 

Quick question: if I reset my controller app am I going to lose all of my Sonos playlists or is this tied to my Sonos account/system?

@thomasbonneau,

All the playlists/settings/services are stored on your speakers.. so when you connect the ‘reset’ controller App back to your ‘existing’ setup you will see everything and not lose anything.

@Ken_Griffiths I’m still receiving the same error message for my account. My wife can still connect no issues. 

But at least now we do not see two separate listings for Spotify under services; now this now just one with our names and drop-down options.  

Small progress.

Any other ideas?

Ugh. And now as feared I have lost access to all my playlists that were shortcutted they are grayed out. And out course recent played are gone. ‍

So for the Playlists section on home screen which before had Spotify Playlists it says content is no longer available and tap to edit to remove from my Sonos. 

Then the native playlist section for Sonos where a Spotify aykist was saved they are all grayed out. 

This is for both my wife and myself on our phones. Same thing with faced Albums from Spotify. 

The playlists are all stored on your speakers - you must be doing something wrong?

Just as an example, if you create/save a playlist to your phone in the Sonos App and login to the same Sonos account on a tablet - you will see the same saved playlist. The controller App is just a ‘remote’ for your Sonos System. Perhaps check the steps again mentioned in my earlier post.

Have you installed and reauthorised both of your Spotify accounts via each of your mobile devices and are the two accounts showing in the Browse Tab of your Sonos app - see if this support link perhaps assists you:

https://support.sonos.com/s/article/3624

I followed the steps exactly. It wasn't too tricky. ;-)

In one screenshot here you can see the same playlists I had previously as they are stored locally as you say; however, they are unplayable. 

The other screenshot shows the Spotify playlist section which previously was on home screen. 

So while you instructions helped to return the multi-account functionality I still can't not browse my library and have some reduced homepage UX on both my and my wife's account. :/

Yes I totally removed and then reauthorized. And yes the UX now splits account properly so this is solved.

But as you see I still cannot browse my library and now have home screen limitations. 

Perhaps make sure you are logged into Spotify, both in the Sonos App service and the native Spotify App too that’s installed on your mobile.

I am most certainly logged into Spotify. And I've tried turning it off and on again.  

Seems I will need to contact Sonos support as clearly there is issue with my Spotify account not properly connecting. Thanks for the help. 

Have you perhaps tried fully closing the App (sliding off screen) for 30+ seconds and then reopening the Sonos App? - that might possibly fix this type of ‘refresh’ issue. 

Does anyone know if Sonos support monitors these forums and assists in opening help tickets or should I just go directly to the chat/email/phone and reference this article?

Go directly.

Yes, they monitor these forums. But going directly is a significantly better way to go. Nothing against the forum folks from Sonos, but they’re both fewer in number, and the asynchronous method is sometimes troubling. 

But either way, you’re not talking straight to a developer, but to a person that will pass on information to the development team. But the folks that you call have access to many more tools to look at your system, particularly if you submit a diagnostic first. Plus, if you give them the ability, I think they can “remote” into your computer/Sonos system to look at things from closer perspective, something the forum folks don’t have access to.