Try wiring the Arc to your router temporarily with an Ethernet cable, then submit a diagnostic and call Sonos support. 
 

Was the Arc powered off while you rebooted the router?
 

Are your surround speakers working? 

Hi, thanks for the comments, the speakers for that were used for surrounded sound working but not with the arc, so disconnected from the Arc.  Arc was on when rebooted router following the instructions for finding the missing product 

Will not be able to connect arc to router via ethernet cable as they are in different rooms and arc cables in the wall so unable to move it closer to the router

Then try a reboot of the Router while the Arc is unplugged. 

Trying to determine if there’s been a failure in the WiFi card in the Arc, but the fact that you don’t have surround speakers connected, or are able to wire the device temporarily isn’t helping, and Sonos won’t be able to tell anything unless the device is showing up in the controller. 

If the above reboot sequence doesn’t ‘fix’ it, we’re at an impasse until you’re able to expend more effort. 

Does sound like internal WiFi failure on the Arc if it will not connect to surrounds either.