Two suggestions.
First, try a refresh of your network. Unplug all Sonos devices from power, then reboot your router. Wait till the router comes back up, plug back in your Sonos devices.
Second, if the above doesn’t work, try connecting one of your Sonos devices with an Ethernet cable to your router. Wait a minute or two, then test.
Once they’re all showing back up, try running the update again. If it fails again, unplug all speakers except the one that failed, and connect just that one to your router, and run the update again. Repeat as necessary to get all speakers updated.
Once they’re all updated, I would recommend that you submit a system diagnostic, and call Sonos Support to discuss it. My guess is you’re experiencing some significant wifi interference which is causing the update process to fail before it completes.
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, there are more options available beyond just the diagnostic analysis.