Best answer by Airgetlam
Note that this error is more about the speed between your speakers and your router, rather than the speed of your router's download capability. And the fact that it's on one kind of stream, and not another isn't all that unusual, actually. Each stream has a different tolerance for disconnects, so some streams will throw that error while others may not.
I'd take a good look at the wifi interference and implement as many of those solutions that might apply to you. After doing so, if none of them resolve your issue, I'd recommend that you submit a system diagnostic within 10 minutes of replicating this issue, and either post the number here, or contact Sonos to discuss it. There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.