Have you rebooted all devices connected to the ‘new’ router? It may be that a simple network refresh might be helpful. I’d be tempted, if possible, to set up reserved IP addresses on the new router as well, just as ‘good housekeeping’. 

However, if that fails, I would recommend that you 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.

Unfortunately, still not happy - after I’ve manually added all IP addresses to my anti-virus (which sometimes has been an issue) - after I’ve had several calls with Sonos support (where I provided diagnostics and let them prowl my laptop virtually) - after I’ve bugged my local ISP, who made whatever gateway changes could be done to my “new” router.

It’s odd that this issue never occurred, even though I bring my laptop to/from work every day (and have for years) and have always seamlessly connected to each “system” without having to reset the controller.  Note also that the iOS app does not have these issues - and automatically recognizes which network/system it’s supposed to connect with.

Hard to provide much assistance past that of those who have access to the diagnostic data, but one thing stands out. Adding the IP addresses to your virus protection application will be of relatively minor assistance, in the grand scheme of things, if you’re having issues with duplicate IP addresses. You’d need to also add them to your router’s DHCP table, in your ‘new’ router. I’d also want to do that network refresh, always something to do when you replace a router. 

Appreciate the thoughts!