Stations do not play on MyTuner

That doesn’t sound too far fetched. Sonos doesn’t have rights/access to stream certain services via the app. However, to be sure I suggest running a diagnostic within 10 minutes of the next occurrence, make note of the reference ID (do not publish it in the community) then contact  Sonos Tech Support. They have tools to analyze the data unless it turns out to be a restricted license service .

There are also certain services that rely on the settings in your Sonos account location, rather than the IP address. I’m afraid it can be complicated, but as a safety measure, you do want to ensure your account at www.sonos.com is set up with your address properly.
 

There have been unsubstantiated complaints on occasion that the account data was ‘corrupted’ and/or switched, and those streamers that rely on that data have had trouble. Of course, I don’t have any idea as to which streamers rely on that data from Sonos as to your location, but as I say, it’s a safety thing to check your account. It at least eliminates one possibility. 

I’ve seen similar behavior where the service works on the phone app but fails through Sonos. Since UK stations work, I’d check the Sonos account region first, then run a diagnostic immediately after trying one of the affected stations. The diagnostic should help show whether this is a location issue or something specific to the MyTuner integration.

The challenge between a ‘phone app’ and ‘Sonos’ is they contact different servers (or ports). The Sonos contacts the server that also runs SMAPI, usually the server the ‘phone’ contacts doesn’t run SMAPI.