This kind of issue usually happens because of your local network problem (it probably got overtaxed). Live audio streaming requires heavy and constant data exchange and communication between your Mac and the Sonos speakers, and therefore needs excellent local network condition to function smoothly.

 

If your local WiFi condition isn't good enough for the task or badly interfered, you can use Ethernet cables to connect your Sonos speaker and your Mac to the same router. And it's NOT recommended perform activities that will heavily tax your local network (such as screen mirroring or downloading) while sending your Mac's audio to your Sonos speakers. 

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This issue usually goes away when the local network conditions improves. If this problem keeps happening constantly in rare occasions, you can always get it fixed by simply disconnecting and reconnecting the Sonos speaker.