I’d try several things first. Try a reboot of the speakers themselves. Also, try a reboot of your router. Check the wifi interference FAQ for any possibilities, especially external to your network. In the two cases I experienced, it was a microwave, and a neighbor with a new WiFi. 

But if none of that works, I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it. But don’t post the resulting diagnostic number here, they 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.

You might confirm (on the settings about screen) that all are on the same version of the firmware.