Sonos connection with xb7 gateway

I think I may have figured this out. Just got an XB7 gateway as well; same connectivity issues with my all my sonos devices. This issue seems to be a combo of a new router + recent app/system updates that Sonos made. The crux of it is that the sonos system seems to get messed up when it's a new router with the same name and password, which causes a whole cascade of devices not found and networks not showing up. Here's how i cracked it: Factory reset all your Sonos devices (process on the sonos website) so that they show green status light. Then go into your XFi app to change your wifi password (annoying, but you just need to change it to trigger this new network setup and then can switch it back). Next, you'll need to hardwire one Sonos device to the router to start setting up the new System. Go through the process to add that device to your Sonos System (hardwired). Once added, go into the Network settings in Sonos and delete any existing wifi networks it has saved, and/or just select your available wifi network with the new password. Now you should have a Sonos wifi network created and you can take out the ethernet cable. You can then change your wifi password back to the old one via the XFi app, and also update in the Sonos App. From there, you can add all the factory reset devices back into the Sonos System via the wifi network. Why sonos can't just detect a new router and cascade the new network information through the system without going through this ridiculous process is beyond me, but seems to have done the trick. Oh, and make sure you're using the new S2 Sonos app if your devices are fairly recent; the original won't work .

Found a bit of a simpiler solution.  Turn off WiFi 6 support on you XB7.  Login to the router, then in the 2.4 GHz band -- change Mode from 802.11g/n/ax to 802.11g/n.  By removing the "ax" you make the router go from Wifi 6 to Wifi 5 support.  You can do this on both the 2.4 and 5 bands.  I only needed it on the 2.4, as my Sonos gear is old enough, it does not use the 5 GHz band.  

Hope this helps!