Next time it happens, submit a system diagnostic within 10 minutes, and call Sonos Support to discuss it. They may want to know which speaker it occurred on, and what source you were playing at the time, and how your Sonos system is connected to your LAN. They’ll be able to tell from the diagnostic which Sonos OS you’re using, which will likely be helpful to know for them to do any analysis as well. 

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.