Have you submitted a system diagnostic within 10 minutes of experiencing this problem, 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 network and Sonos system.

It magically reappeared after I restarted the Roam...

So the solution proferred by Sonos was to reset the S2 App (which worked) and the Windows Controller App (which didn’t)

And now Sonos have suggested unplugging everything…..again

And resetting everything again…..etc etc

Ad infinitum

Its likely your Roam, or phone, has decided to switch between 2.4 and 5GHz wifi, and your router is unable to route between devices on different frequencies. You can verify this by looking at your router admin pages when the problem occurs. Then buy a smarter router.

Sonos should not be suggesting to reset everything.  Resetting is useless 99% of the time, and wipes out important diagnostic data 100% of the time.

Anchorman vibes :)