Given up trying g to use their app and control directly via Spotify or Google home. You wonder what the beta testers were doing…

Networks are continually changing, that’s their design. There is no ‘static’ network. And your ‘internet speed’ is a measure of the connection between your router and the outside world, and has almost nothing to do with the speed of the devices to your router. 

Networks are subject to outside influences as well, not only ‘inside the network’ stuff, as noted by the data in the wifi interference FAQ.  I certainly have experienced this, with a new neighbor setting up a WiFi device using the same channel as I was using, as well as receiving more transitory interference from an old microwave, that was ‘leaking’ RF while operating.

Much as any electronic device, routers are also sensitive to power fluctuation. Were I to hazard a guess, your router may have handed out bad IP addresses the last time your Sonos rebooted, and requested a new IP during the last firmware update. 

Fairly easy to fix, at least temporarily, by unplugging all Sonos devices, then rebooting the router, waiting a couple of minutes, then plugging back in your Sonos. Not only does this have the benefit of refreshing the router, but the Sonos OS as well as getting new IPs. Of course, if you prefer the more ‘permanent’ solution, you can check your router’s manual and set up reserved IP addresses in the router.