Get the problem to reappear and send in a Diagnostic. Once sent contact Sonos Support directly and they can look at the internal data we users can’t see.

This is not as surprising as you seem to think it is,  The app on your PC is not playing the music.  No Sonos app does that.  It sends a command over your network to a speaker telling it to fetch music from a particular source.  Whether the files are stored on the same PC as the controller or a different PC makes no fundamental difference - that is how Sonos works.

How does your PC connect to your network?  Wired or wireless?

I’m not suprised, Sonos historically had alot of connectivity issues with their software based on a codeforce prioritielist that does not include a seamless smooth user experience but more pushing new products by discontinuing old ones in the software - oh and also pushing adds in the app. Basicly sonos is garbage. I am connected wireless, and everything else is 100% working fine, i tested, many times having other streaming services running simultaniously just so that i would have a visual confirmation if the connection should drop, that never happend, the other streaming service ran smoth and seamlessly for as long as they were open. Sonos on the other hand still did not function at all 80% of the time and struggled for the remaining 20% but i guess, was basicly working. 

My system has worked seamlessly for 11 years.  Now 14 devices in 7 “rooms”.  Streamed or from NAS music library, all fine.  I guess I have been lucky.  I shall leave you to your opinions.