Ok, so, not a web app, but the Sonos S1 windows app. The only reason I can think of for it to stop working on one machine, but continue working on another is the possibility of something blocking the ability of that computer to reach the speakers, which implies some sort of VPN, port blocking, or even a ‘work profile’, which often includes one or both of those. Have you tried to submit a system diagnostic, and call Sonos Support to discuss it? Even if you can’t submit that diagnostic from the Win 11 machine, I’d definitely call in to get assistance in diagnosing why one machine works, and the other doesn’t.