There’s at least two possibilities that probably cover 99% of the cases of this. The first is simple wifi interference. Read that linked FAQ, and take a look in your home and outside for potential issues. Note that I’m a home theater context, the surrounds and Sub(s) are connected to your sound bar using a special 5Ghz signal, and not your normal Wi-Fi.

The second is possible duplicate IP addresses. While those extra speakers are getting their signal from your sound bar, they’re still getting IP addresses from your router, and due to the way Sonos reboots their speakers during an update, and request new IP addresses, they frequently expose a router that’s gotten into a ‘bad’ state. Easy to confirm, just unplug all Sonos devices from power, then reboot the router. Give the router a couple of minutes to reboot, then plug back in the Sonos devices, starting with the sound bar. If this fixes the issue, I’d heartily encourage you to read the manual for the router, and figure out how to reserve IP addresses for your Sonos devices, as that tends to help this type of issue from reoccurring.

However, if neither of those solutions fix the issue you’re experiencing, I would recommend that you submit a system diagnostic within 10 minutes of a repeat of 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.

Thanks for this I’ll try tomorrow .

Now 4 days after restarting  router and switching off units as you said all working  thanks.

As I said, I’d heartily encourage you to read the manual for the router, and figure out how to reserve IP addresses for your Sonos devices, as that tends to help this type of issue from reoccurring.