Please post the url you are having trouble with.

Actually, all of them.
Two examples:
https://streams.egofm.de/egoFMBW-hq
https://play.adtonos.com/thisisprimordial
(And another one that contains personal login data which I’d rather keep, well, personal.)

When trying to play one of those on the OneSL, it blinks white once and orange twice. That is the only maybe meaningful error message I got.

When trying to play through the S1 app, the “play” button turns to the square stop and immediately back to play. No waiting circle, no buffering time, nothing. It's different than when internet is choppy or the station is down…

My current solution would be to hook an old phone up to the line-in and stream on the phone, but oh my...

Sonos plays audio streams: these are not streams, they are web pages. Sonos is not a web browser.

The first one uses a stream of https://cast.egofm.de/egofmbw.mp3?ar-distributor=ffa0&aw_0_req.gdpr=true

The second one is https://fr1-play.adtonos.com/8108/thisisprimordial

I have checked neither of these in the Sonos app, there may be other reasons they don’t play (headers missing, auth, codec, streaming format), but they stand a better chance than a web page.

Funny thing is - exactly these webpages worked before just fine. Also I think that they're just redirects, not actual webpages, but that's semantics.

Also, they still do work in tunein, vlc, basically anything else that plays streams.

And, the actual stream that I'm having trouble with is not a redirect URI or a webpage but that is the actual URI of the stream that has worked for the last ten years with Sonos (via tunein). Nothing about that stream changed. It’s 32bit stereo 44,1KHz MPEG AAC Audio stream (or so VLC tells me), so Sonos should be able to handle that (like it always did).

Do you happen to know a streaming URI that 100% works that I could test? I'm pretty sure that it's not an issue with my network, I still think the March 9th update of the Sonos hardware broke something (funny that the old hardware gets updates at all).

Both stations play fine for me on S2 with the links originally provided by Stefan so I don’t see why they shouldn’t work on S1, especially if they worked before. I don’t have an S1 system to test though and the only thing I could imagine being the culprit here is an SSL issue, because S1 doesn’t support the same things as S2.

Today I’ve had a long and actually quite pleasant conversation with Sonos support, and after ruling out any problems on my part (network configuration etc), they said that there is an issue with tunein-streams they're aware of and trying to fix (understandably, they didn’t give me any nitty-gritty details).

That may well be the issue. I haven’t checked all of them, but one stream that no longer works is an http link, whereas one that still works is https. (I also have a Sonos One SL.)

Interesting, I would it expect the other way around but maybe the station has shutdown the http stream all together.