Sounds like your speakers are having trouble maintaining a connection with the MixCloud servers. The first thing I’d try is a network refresh, by unplugging the Sonos devices, then rebooting your router. Wait two minutes, then plug back in your Sonos devices. Wait another two minutes, then test.
If the issue continues , it may be worth checking for wifi interference .
Alternately, you could submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it. Don’t post the resulting diagnostic number here.
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.