This is normally down to poor connections between your players.  How are you connecting your Sonos devices? (Wi-Fi or Ethernet)  

Please follow the steps in this article and let us know if the problem persists: Music service audio stops or skips | Sonos

I have one unit plugged into the router and that connects to the rest via WiFi. It happens more if you skip a track, it cuts in and out on some speakers whilst continuing playing on others