Okay, so apparently there is a difference between Sonos Radio and TuneIn. After I wrote this post I went and double checked how I actually started playback of this radio, and I had it added as a favorite since a long time ago. 

When actually searching it and starting playback from the Sonos Radio section, the playback seems to work much better (occasional stutter, but not the permanent stutter after 2-3h). Whereas my old favorite will start stuttering right on the money after 2-3h. I didn’t make a long run test with the actual TuneIn service (which still exists? confusing to say the least).

The difference in AVTransportURI between them is 

 

x-sonosapi-stream:tunein%3a9767?sid=303&flags=8224&sn=20 (working, Sonos Radio)



x-sonosapi-stream:s25681?sid=254&flags=8224&sn=0 (defunct, will stutter)

Sounds to me like this is some legacy streaming code that someone forgot about and is buggy, but still exists? Also, Sonos Support would have seen this in the diagnostic but couldn’t give me this solution which is also a huge let down.

Favorites can get stale, so re-creating them helps when the url changes. However, this is not really what is happening here.

The “sn” change is just the ‘SerialNumber’ which is the index into your local list of services - TuneIn was your first service (=0). The ‘flags’ are the same, which means the underlying stream format is identical.

The real change is that these urls go to different services, so the playback change is likely related to that. 

Sorry after i posted I realized who the OP was, sorry for mainsplaining the urls, you know this stuff at least as well as I do.

Haha, no worries man. It might be educational for other readers anyway.
 

I’m glad an relieved that this at least was solvable. I’ve seen at least one other post (which dates a few years) with someone having the same issue as I, but there was no resolution to it. Hopefully this helps someone in the future. 

Not sure if I should start a new topic. I have a similar issue and it’s so frustrating. Happens on my Arc Ultra when playing Vanilla Radio - Smooth Flavour on Sonos Radio. I haven’t kept track of the timing but it happens after a few hours of listening. It starts jittering a lot, mostly playing artefact noises, and sometimes the soundbar becomes unresponsive to voice commands. 

Stopping the stream and starting it again solves the problem for a few hours.

Not sure what to do about this, some tips would be greatly appreciated.

Start a new topic, you’ll be better off in the long run.

In the meantime, I’d try a couple of things. Well, maybe one, which contains all sorts of potential actions/fixes, which may or may not help.

Unplug your Arc Ultra from power, which may or may not be the easiest, but will likely help. If you have other Sonos devices, unplug them too. Reboot your router, and wait two minutes for the router to come back up before plugging back in your Sonos. 

Wait a couple more minutes before ‘testing’, just to give the Sonos to properly boot up and reconnect, before trying Vanilla Radio again. 

If/when it fails/starts stuttering again, within 10 minutes, submit a system diagnostic, and call Sonos Support to discuss it. Don’t post the resulting diagnostic number here, they get sensitive about GDPR.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.