The Arc reserves it’s 5GHz radio for communicating with surrounds/sub, so will only connect over 2.4GHz

See https://support.sonos.com/en-gb/article/sonos-system-requirements

Sonos soundbars use 5Ghz for the dedicated link to surrounds and Sub. They therefore do not do 5Ghz for normal connections (even if no surrounds or Sub are bonded).

Okay so does that mean if I were to ad a sub or surrounds I could then stream music to it again?

You need to connect the Arc to 2.4GHz or else wire the Arc to your router.

Okay thanks so much for clarifying this!

So, if I connect the Arc to 2.4 to be able to transmit, it will disconnect from the Sub and Era 200? Or it can use both bands at the same time?

It can use both. The Sub and Eras will still connect to the Arc’s 5GHz radio when the Arc is using the router’s 2.4GHz band.

Would be nice if they mentioned this somewhere in the “technical documentation”!

I am having a similar issue, sort of. My Sonos system stopped working after I upgraded my internet to fiber, when I did that I performed a system update on the nighthawk firmware, since then nothing works any more. I wound up seperating the 2.4 (SSID) and 5G (SSID) then enabling multi detect but it will not allow me to reset it up with my phone being on the 5g network. So, I tried using the 2.4 on my phone to setup the system again, and I get all the way to the last part and it comes up with more info saying 802.11 b or a network now b or c? /pfft In the depths of the manual for Netgear you can locate nothing about that. I even tried wide open security, and nada. I have a sonos arc in my living room with a base, then in the bedrood I have a mini arc, 2 solo 1 speakers and a mini sub, on the lanai I have a sonos 1 amp that powers a couple of outdoor high output speakers. I had all of it working together, except the older unit which I could still control using the old app on my phone.

Any ideas on what to try would be so much appreciated, grateful to have located this space and trying to look where I may also contribute. - Daniel 

https://support.sonos.com/article/supported-wifi-modes-and-security-standards-for-sonos-products

Which Netgear Nighthawk kit? 

Also see https://support.sonos.com/article/supported-wifi-modes-and-security-standards-for-sonos-products

https://www.costco.com/netgear-%E2%80%93-nighthawk-ax5400-wi-fi-6-router%2C-one-year-advanced-internet-security-included.product.100948104.html#:~:text=NETGEAR%20%E2%80%93%20Nighthawk%20AX5400%20Wi%2DFi%206%20Router%2C,Internet%20Security%20Included%20Compatible%20with%20All%20WiFi

Netgear kit is typically pretty docile.

Did you reboot (i.e. power off and on again) all the Sonos units after the post-firmware-update router reboot?

Have you tried a router reset and reconfiguration? Sometimes Netgear firmware seems to benefit from it after upgrade.

Thank you for the reply, yes, I powered everything off, then started the modem, router, arc, sub, one, etc. It goes though setup now, then at the end it stops at the last step and says that it should be an A or B network, not an N? 

Try this:

Resolution - via routerlogin.net

1. Navigate to http://routerlogin.net/

2. Sign in using the router's administrator username and password.

3. Click on the Advanced tab.
4. 

5. From the side bar menu, navigate to Security > Access Control (see image below).

6. Locate the blocked Sonos component in the list showing in the middle of the page (as shown in the image below).

7. Add a checkmark on the checkbox on the right of the blocked device.

8. Click on Allow, then the Apply button above. 

    

Resolution - via the NightHawk app

1. Launch the NightHawk mobile app.

2. Tap on Device Manager.
3. 

    

4. Locate the paused Sonos device.

5. Slide ball switch to the right to unblock the device.
6. 

Once completed, the Sonos Player will be able to connect, register, update, or stream. You may need to reboot the affected Sonos component(s).

No paused device for Sonos, sheesh.. thank you for the effort. I am researching further before taking any other action. One of my simple issues is the location of my head end now, I need to run a few cables to hardwire to the router I think. Man I miss my sound.. ugh 

Give Sonos Support a call. 

Ha! They’re befuddled as all of us, getting a long enough patch calble to manually hook one up

I had a similar issue with a smart fan. In the end it only worked when I logged into the modem, switched off 5ghz and only activated the 2.4. Than it would connect and after that I switched on 5ghz again and it worked. If you necessarily want to keep it off so your devices will always connect to 5ghz, than make sure you separate the two via the settings when u log in to your modem. Your IP should have a manual for this. After separation, you can give the 2.4 network a new name. When this is not an option, you can use a second router to still be able to have devices connected to a 2.4 ghz network.