Most Speakers are Gone and I can't Re-Add Them

Sure. Based on your comments, the Sonos weren’t powered off when you rebooted your router. Try that. 

If it doesn’t work, it would be helpful to this community to know the type of network you have, and the make and models of your router and modem.

Alternately, you could submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it. Don’t post the resulting diagnostic number here, their lawyers get sensitive about GDPR.

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 Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

Oh, please don’t factory reset any devices. It’s not really a solution, and should only be done at Sonos’ direction.

Thanks for the quick reply.   To clarify, are you saying I need to go unplug ALL of my Sonos devices and then reboot my router?   It can be done but that’s quite an exercise in this setup.

Also, relative to your question about equipment, I have an Xfinity router set to Bridge Mode feeding Google Nest WiFi points by ethernet.   This is the same setup I’ve always had so nothing changed there.

Sadly, I have a long history of factory reseting Sonos devices as they constantly seem to drop out and it’s the only way I’ve been able to get them back.   It’s only now that it’s stopped working.

Any additional thoughts would be much appreciated.

Prior to this current mess had you reserved IP addresses for the SONOS units? 

Have any of your units not been Factory Reset? Don’t Factory Reset these units because your recovery will become more difficult.

I’m not sure if your profile listing of your SONOS components is accurate. If they haven’t been Factory Reset, try wiring a PLAYBAR or AMP to your network.

Factory reset is almost never the solution, aside from a couple situations described in the support FAQ. It will erase data Sonos support may need to help you and it may mask an issue, not due to the reset but to the accompanying reboot.

Seeing this

 couldn’t find any Sonos products on your mobile device’s network

It makes me wonder if you have something on your phone blocking the setup. Spam filters, DNS blockers, VPNs and such should all be disabled during setup. Once done adding rules to allow Sonos to communicate is a good idea.

The "refresh" is very picky, ALL Sonos must be powered down, then reboot router and controller. Once they wake up then power the Sonos back up.

Even with all that, and more,  y setup was still iffy, the fix was to use the routers DHCP server to set static/reserved addresses for ALL Sonos, followed by one more network refresh to lock in the new addresses.

Based upon the above statement something changed three (3) months ago with your network whether you realize it or not. My first thought is that somehow the Xfinity router side of the modem (as they are contained in one box) is broadcasting a WiFi signal and is no longer in Bridge mode. As you say you did nothing then Xfinity/Comcast either:

1. Remotely made an update to it’s equipment that changed the settings
2. Xfinity/Comcast outages (which they have a lot) disrupted the settings

Reference #2

• I dropped the Xfinity side of Comcast which supplies the internet in favor of Google Fiber.
• I still use the Comcast side for cable.
• I no longer have an Xfinity Router/Modem so no need for Bridge Mode.
• Most people don’t realize that they can drop Xfinity for Internet and still use Comcast for cable.
• My monthly cost for Google Fiber and Comcast Cable are the same as when I used Xfinity/Comcast for both

I digress, so back to your issue. I strongly suggest you verify that the Xfinity/Comcast box is still in Bridge Mode. 

Also, verify that your Google Nest Wifi points don’t have DHCP capability to assign IP addresses. Only the main node in the Google Nest should have DHCP ability. 

Also, the Google Nest satellites should be wired to the main Google Nest Node and not to your modem. If they are wired individually to your modem then you have multiple Wi-Fi networks. Not Good.

Stop factory resetting your speakers. It’s only a temporary fix as you have surmised.

When I initially installed SONOS there were issues with my network and my education. There were multiple Factory Resets until I got my education straight. Since then there have not been any mass resets. That was in 2005. Over this period there have been multiple moves, changing ISP’s, ISP failures, network hardware changes, but no mass Factory Resets.