That error message has to do with your internal WiFi / LAN, not the speed of the internet to your router.
You haven’t said which music service you’re using, but I’d try a network refresh. Unplug your Sonos devices from power, then reboot your router. Wait a few minutes after rebooting the router, then plug back in your Sonos devices.
If that doesn’t 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.