Era 300s wont connect to Arc for Surround

What other troubleshooting steps have you gone through so far? Has the Arc/Eras already been factory reset for example? Have you tried a different router (if you have another available) or have you already recently switched or perhaps factory reset your router?

I ask those few things, because when ‘bonded’ the Era surrounds each connect over a 5Ghz direct wireless connection to the Arc and their IP addresses are assigned by your router, but proxied via the Arc. A few routers can have issues with the proxying of the IP addresses and sometimes a router factory reset can occasionally resolve the matter, but it would be nice to know more about what action has been done so far. 

I’ve factory reset the eras, unplugged and replugged them in at least two dozen times, unplugged and replugged the Arc, reset my router and modem. 
 

The Eras were set up and connected as surrounds, and then mysteriously today became an issue. 

What make/model is the router?

To perhaps save time communicating back & forth. Here’s my first suggestion…

I’m guessing you factory reset the Era speakers before first removing/unbonding them from the Arc? I’m just wondering if the Arc perhaps thinks they’re still bonded as ‘offline’ surrounds? 

It seems you’ve reset everything so far except the master HT device, so maybe consider an Arc factory reset, but do not (ever) reset all your speakers in one go, as you could lose all your system settings - you need to leave one speaker setup and working in the Sonos App so that it retains all your settings.

Once the Sonos Arc is added back to your system, try ‘bonding’ the Era’s again to it. Hope that works for you. 👍

How do you mean by “master HT device”?

have you experienced this before with your system and was this the fix? I do appreciate the assistance but am really looking for someone who has experienced this and/or fixed this issue versus more guessing, after having spent 4 hours doing that already today with Sonos. 

The HT ‘Home Theatre’ device - which is your Sonos Arc controls the secondary devices when they are bonded to it. The secondary devices in your case are the Era’s - your system was setup and working okay and you mention you have already factory reset your modem/router, the two Era devices, but so far you have not factory reset your Sonos Arc, so it makes sense to try that next.

As mentioned when bonded as a HT setup, the Era products switch and communicate with the Arc over an Ad-hoc 5Ghz wireless connection and the router DHCP IP addresses are assigned by proxy, via the Arc, to the Era’s - if your router has been reset then one assumes the DHCP server is working correctly as your Era’s and Arc are working okay when they are not bonded - so my suggestion is to next try the one thing that you have not done already and that is to factory reset the Arc - as that’s the device responsible for the proxying of addresses and the ad-hoc wireless connection. 

Sorry but I thought you were looking for suggestions to save you waiting for Sonos Support? If you don’t want to go down the suggested route then that’s fine and perhaps you are best to wait for level-2 Sonos Support to get in touch with you next Monday. I’m just expressing a view of what troubleshooting I would have tried in the meantime.

I appreciate the help. I will try resetting the arc and see if that works. 
 

the Eras stay working when they’re not set up in surround, but now when I try to connect them as surrounds I get the “not connected” error, so I can see why that might make sense. 

I’ve now factory reset my arc, and still cannot get my era speakers to connect back as surrounds. They still work separately though. 

Ah well it was worth a try - can I just ask what router you are using and do you know if it’s firmware was recently (auto)updated?

Also, I assume your Era-300’s are not stereo paired at the moment.