I’d look at a several things. First, I’d double check the account location settings at www.sonos.com, and ensure they’re set properly. Likely they are, but it is worth double checking. Next, I’d reboot both the router and Sonos devices. I’d also double check for any potential software that might be port blocking, like work profiles, VPNs, virus protection, etc. Finally, if none of that works, I would submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it. But 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.

I did everything you said apart from calling the support staff as I had not been home in the available hours this week. It still did nok work… until I randomly decided to try again late last night and it got through.

thanks for the help. Still confused, but something worked, so I am happy.