It seems like you’re having issues between your controller device, your router, and the speakers.

The reason the Beam works during this is that it is hardwired to your TV, and doesn’t require internet, although the surrounds would.

I would try this first. Unplug all of your Sonos devices from power, including the Beam. While they are all powered off, reboot your router. Give the router a couple of minutes to come back up, then go ahead and plug all of your Sonos devices back in. Give them all a couple of minutes to boot up, then open the controller and see if they all show up.

If they don’t, connect any one of your Sonos devices to your router with an Ethernet cable, then wait a couple of minutes for that process to spread across the network, and then try opening the controller app again.

I’m hoping that you don’t have any Wi-Fi extenders, access points, or mesh networks set up. 

Just reread your post, if you have to run an Ethernet cable temporarily to help troubleshooting, it needs to be connected to the Beam, and not one of the surrounds. 

Having this problem- after adding xFinity xfi pods (mesh network). What is the special issue with mesh networks referenced in prior post?

Mesh networks seem to work best with Sonos in Wired setup, with one Sonos speaker (or a Boost) wired to the main router hub.  

See this link:

https://support.sonos.com/s/article/3235

Moderator Note: Link updated

Thank you very much. This was very helpful.