That’s a lot of exclamation points!

You have got a couple of things to look at, based on the information provided. The first is the information in the wifi interference FAQ. Remember, however, not all interference comes from devices that are in your network, or alternately are in your home. On two separate occasions (and locations), I’ve had to deal with a failing microwave ‘leaking’ interference, and a new neighbor with a new router location and channel. Fortunately, at least for me, sunspots have not yet been an issue.

Second, there is the possibility of duplicate IP address issues causing interruptions in the data being received by your speakers. The potentially shorter term solution to this is to power down all Sonos devices, and while they’re powered down, reboot the router. Give the router a few minutes to come back up, and plug back in the Sonos. 

Of course, any router that has gotten to this state once can do so again, so the longer term solution is to assign reserved IP addresses for all Sonos devices in the router. The instructions on how to do this would be in the router’s manual, each company seems to do it slightly differently, and there is no way to force this in software by Sonos. 

However, these two possibilities are only the most likely of the potential issues. If neither of these suggestions work, I would recommend that you submit a system diagnostic within 10 minutes of experiencing 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 network and Sonos system.

@siwaldron,
You ask if it might be your router, but what router is it - make/model? Perhaps describe your network setup in a bit more detail. Are there any other WiFi access points, WiFi extenders, etc? Any switches, (managed, or unmanaged)?

What mobile controller device are you using, and is the device using any security software, or features, such as MAC address spoofing, VPN client, or a firewall App etc?

When the Sonos devices are not showing in the Sonos controller App, are they actually still connected to your router/network subnet and do they still have an IP address assigned? If they are still present on the LAN, it might be a case that the SSDP multicast ‘device discovery’ packets between the controller App and your speakers are ‘perhaps’ not working as they should be. So yes, it could the router, or a setting on the router, but it could also be plenty of other things too on your local network, or controller device.

My first step would be setting the static/reserved IP addresses for all Sonos using your router’s DHCP Settings page. It is usually quick and simple and many routers even have a help button on that screen. Once done power down all Sonos, reboot the router and power the Sonos back up. Even if it wasn’t your problem you have hurt nothing and taken a hard to diagnose issue off the table.

Second would be the WiFi interference process. Don’t over look the “too close” issues, under a meter. Also trust nothing, many devices that don’t have a radio can put out amazing amounts of RF noise. My WD hard drive would stop a playing Sonos if moved within 2 feet and cause glitches at 3. 

Once the two are done and if you still have the issues the Sonos support call is in order. You could do it first but this time of year they are busy so self-help first can be a time saver.

Many thanks one and all. Yes lots of exclamation points - I’m not technically minded so I find these things intensely frustrating, but you comments have provided me with a lot of help and focus so I’ll get back to you on the details once I have given them a go, many thanks