Having the same issue - appeared out of nowhere. 
 

“Alexa Cancel” does NOT work for me, nor does “Alexa Stop” or “Alexa Pause”, but “Alexa Pause MUSIC” or “Alexa Stop MUSIC” does work. 
 

Maddening how things that once worked flawlessly can seemingly spontaneously malfunction. 

Same problem, with my Sonos 1. Can’t find any command to stop/pause/cancel, so have to do so via the Sonos App

The first thing to do is Disable then Enable the Sonos Skill within the Alexa App.  Can you confirm if the issue persists after you have tried this?

Yes, raised a ticket with technical support and this is now resolved. Deactivated the skill after removing Alexa from the Sonos One. Reenabled both and it now workd

I’m having similar problem - playing a playlist from Apple Music on my Sonos One and it won’t respond to anything; tried pause, stop, set volume to 1, turn it down, turn it up... 

please confirm which technical support you raised this with? Sonos or Alexa? 
I will do the same and post any updates I get. 

It was with Sonos

I’ve got the exact same problem. It used to work though, but all of a sudden Alexa is not stopping anymore. I tried “stop”, “pause”, “cancel” with and without room names: it just won’t work. I’ve received a new One and set it up in the dining room: it doesn’t work either. The beam attached to the TV also acts weird: it stops when I switch the TV off, but then starts playing the TV sound (with the TV off) 5 seconds later.

I tried all sorts of stuff: removing Alexa from all my Ones and from the Beam, deactivating the skill, etc. Still doesn’t work...

Hi 

Can you open the Sonos App>Settings>Services>Amazon Alexa and then select each product in turn and remove Alexa.  Power down each device and then repeat add this time add Alexa to each device.  Let us know how you get on.

Using the Sonos app on my iPhone, I went into Settings/Services/Voice and removed Alexa from all devices. I powered off my 3 One’s (2 of them are paired), my Beam and 2 Play:1’s paired for 5:1, my Bridge and my Connect. I closed the app, powered on all the devices, opened the app and added Alexa back to the Beam, the paired One’s and the other One. And … it still doesn’t work.

Hmmm. If you ask Alexa, what is the time? Does she answer correctly?

Yes

I wonder if this is a duplicate IP address issue. Can you power down these devices, allowing to boot before moving to the next:

- Router

- Any wired network devices

- Any wired Sonos devices

- Any other Sonos devices

- All other network attached devices.

My Sonos Bridge is wired to the router via ethernet. All other Sonos devices are wireless into the Bridge (i.e. if I switch the Bridge off, they cannot be accessed).

All Sonos devices have a static IP address going from 192.168.1.200 to 192.168.1.207.

I’ve switched off router and Sonos devices, then back on one at a time, starting with the router, then the Bridge, Connect, Beam, 2 Sonos Play:1’s, 3 Sonos One’s. They all come up with their own IP address as expected.

… And “Alexa, stop” still doesn’t work.

Hi.  Okay, can you submit a diagnostic and post the number in this thread?

Done - from the mobile app.

Ref. number: 1646197812

Please see this article:  https://support.sonos.com/s/article/141?language=en_US

Thanks for your help UKMedia!! Really appreciate.

Ref. number: 1646197812

No probs Sonos staff should investigate this pretty soon.