I recently changed providers from BT to Sky so had to reconnect to the new router. Similar problems and followed all the instructions and finally got connected. However, when using my iPhone 12 and airplay, the whole system would drop out usually during the first song and I had to reconnect again and go through all the hassle.

Perhaps not much help to you but I finally cracked and connected my Beam 2 directly to my Sky router using an ethernet cable. I can now use my iPhone/airplay and have had no drop out. 

I’m wondering if this helped to reset things as I appear to have greater functionality in the Sonos app (for example, before I connected via the ethernet, I wasn’t able to set up my Beam for the room it was located in). If I could be bothered, I’d now see if things worked if I disconnected the ethernet cable and relied on wifi alone.

Like I said, perhaps no help but perhaps worth a try.

Note that rear (surround) speakers don’t connect directly to your router, they instead connect to your sound bar, and get proxy IP addresses from your router through that connection. 

It sounds like in some manner, you’ve factory reset the Beam, if the system is recognizing it, and asking you to add it to your Sonos system. However, if that’s the case, it should not be recognizing any surround speakers, unless they’re normal Sonos ‘room’ speakers, and not set up as surrounds yet. 

Have you tried to call Sonos Support directly to discuss it? It seems like you just have a configuration failure in your network, but there’s not enough detail to tell, the Sonos support folks would have a better opportunity to assist than those of us in this community forum. 

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.