Frustrated with Sonos not talking to each other

Power off all the speakers and your router. 
wait a few minutes. 
Power up your router. 
Wait for it to fully restart and for the wifi to start. 
Power up the Arc. 
When it’s fully running, power up the Sub. 
Keep going one speaker at a time until all are running. 

The suggestion from @nik9669a will clear any potential duplicate IP addresses, as well as reloading the firmware for both the router and all Sonos devices. Never a bad idea. And it certainly might fix the issue. 

Your symptoms are a pretty clear indication of either enough wifi interference to block grouping, or some setup issue, perhaps in the router, blocking the speakers from talking to each other. There’s not enough information to really hone in on a solution, so I would recommend that you submit a system diagnostic within 10 minutes of recreating 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 Sonos system and network.

Been there done that.  I’ve inspected the IP addresses and no conflict.  I got a three station Netgear Wifi 6E mesh network for a 3000 sqft single family home.  All the Sonos systems are on the first floor.  I did the system diagnostics and sent to support  - all they could say is that there is RF interference.   We have no RF besides this mesh network on our lot.  I can see a handful of neighbors wifi but they are weak signals.  I’ve had and used Sonos since almost day one, replacing my system with v2 when it was necessary.  I’ve never seen anything like this.  I can’t build routing tables by converting IP addresses to binary octets, but I am pretty familiar with routers and basic network engineering.  It is really upsetting as all I want to do is listen to music.

Not sure which “been there done that” suggestion you’ve tried. 
 

Are the three Netgear stations locked to the same channel, and is it different from the Sonos channel?

And, are all routers set up to use the same subnet, so the Sonos devices can ‘see’ each other?

Sorry was referring to powering everything down and then powering up the router / powering on the sonos speakers one at a time.

Yeah, everything is on the same channel.  Additionally, each speaker is on WM: 1 except the surrounds and subs are on WM: 2.   I have a Sonos Boost but quit using it because I thought the Netgear Mesh would be better - I was having similar problems with the boost as well but maybe I’ll try re-introducing it again.

Only other thing I can think to do is to factory reset each speaker and rebuild the system - but man that’s a pain.

Yes. 

It does seem strange that all was well until you changed to the Netgear system. 
 

Can you, at least for test purposes, run an Ethernet cable to any of the speakers? 

I’m still a little concerned by your statement ‘We have no RF besides this mesh network on our lot. ’. RF interference doesn’t have to be from WiFi sources, and then you state ‘I can see a handful of neighbors wifi but they are weak signals.’ further reinforcing the idea that you’re not considering other sources of interference other than WiFi.

But I’ll step aside, and let @nik9669a work with you. 

The grouping error message appears to be because, despite the controller being able to access each player individually, for some reason they’re not able to connect with one another.

It would be worth checking whether all the devices involved are attached to the same, or different, Orbis.

Sad to say, in a way, but it might indeed be better to wire a Sonos unit to the primary Orbi. There is at least predictable L2 behaviour on SonosNet.