You must also have WiFi coverage issues for other devices. Time to invest in a WiFi mesh. You can then connect your Sonos units as well as get decent coverage for mobiles etc.

Thanks!  Yes we have super fast wifi and a Google mesh system.   Not sure why it plays up to be honest but sometimes it just fails to connect to the app.  

Your Google mesh contains a router in its primary node. Assuming you have an ISP-supplied router you’d therefore have two subnets in your home network: one upstream of the Google primary, and one downstream on the Google WiFi. Sonos controllers and players need to be on the same subnet.

I’d suggest you either disable the WiFi on your main/ISP router, or make absolutely sure your devices can’t ever connect to it by removing those WiFi credentials.

If you want to retain the Boost it should be wired to a LAN port on the primary Google node.