I’d try the “fix it” first. After that a reboot of your phone, router and (one by one) the Sonos devices.

So all I had to do was power cycle the Beam (gen 2) and they all showed back up. Somewhat annoying though as this happens maybe once a month. Sound will be coming out of all speakers normally but the app is not “finding” them. I can see they are working through my router so I don’t believe it is a router issue. Seems to be something with the app or the Sonos network maybe?

More likely an issue with your router, and its DHCP table. Rebooting the Sonos forces it to request a new IP address from the router. Try assigning the Beam a reserved IP address in your router, see if that resolves the issue. 

Beam and all surrounds have all been assigned an IP for quite some time. I noticed that there was an app update which I updated this morning so maybe that had something to do with it.   Thanks. 

Interesting. The next time it happens, I would recommend that you submit a system diagnostic, and call Sonos Support to discuss it.

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 phone folks, they have tools at their disposal that will allow them to give you advice specific to your Sonos system and network.