Hard to tell, but it’s possible it’s a DNS issue, Before contacting Sonos, I would certainly try a network refresh, by unplugging all Sonos devices from power, then rebooting the router. Then wait a couple of minutes before plugging in the Sonos devices.
However, if that doesn’t change anything, I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it.
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.
I have the same issue on my Beam (Gen 2). So it’s not an isolated issue. It happens every time I use the Sonos app, and sporadically when I use Alexa to start the playlist. What’s most frustrating is that the speaker won’t respond to anything after it stops when I use the app. I have to shut it off and turn it back on in order for it to accept an other input.