First: As you have discovered, Factory Reset is a waste of time for this sort of issue. Refrain from Factory Reset without further consult.

Usually, a simple reboot of BEAM and CONNECT:AMP will work through this, at least temporarily. Reboot all of the SONOS components after the rebooted router comes back online.

Always look for silly stuff, such as disconnected wires. (been there, done that, after a head slap). Or playing content that does not include surround.

Have you made any recent changes to your network, such as adding a new “box” or replacing the router? On occasion a SONOS update will trigger an issue, but a simple router and SONOS reboot will work through this. If you have not done so, after rebooting the router and SONOS units, I recommend that you open your router’s Admin panel and “Reserve” IP addresses for all of your SONOS units and any other regular network clients.

Describe your system for us. What is wired? Wireless? Router model? Wireless extenders, mesh points? Other components on the network: such as TV’s, thermostats, cameras?

And, we cannot rule out a hardware issue with CONNECT:AMP.

If none of this resolves your issue, I suggest that you submit a diagnostic, note the confirmation number and contact SONOS support. The diagnostics contain details available only to SONOS staff.

the problem was that I could not add my 2 SL one spkrs. as surrounds with my beam. Even though the app said they were connected no sound was coming through. I had tried everything I read online so had to call in. 
The solution was to unplug the Beam and both speakers then when I plugged them back in everything was working. 
Since the Beam had been working all along I didn't think of that.