Have you tried deleting and reinstalling the Sonos app or rebooting the Mac?

I’d be tempted to delete and reinstall, too, making sure to ‘connect to existing system’ when prompted. I don’t have this issue on my M1 Mac. 

Have deleted and re-installed several times.  Program finds and “works” system with no difficulty. Speakers in ten rooms all are found and connected. Have rebooted several times . All basic “app repair “ moves done but no change in this fairly disruptive and quite maddening performance. Have reported to Apple many times.

Have you tried submitting a diagnostic to Sonos, as well?

Since this isn’t happening on my multiple Macs, I have to wonder if there’s something local interfering with the ‘quit’ command.

I have deleted SONOS from the Mac I most often use on the net which is the one with the problem.  My thought is that my VPN (Lockdown) is blocking trackers used by the program.  Trackers blocked include Amazon, crypto mining, Data trackers, email trackers,Facebook, WhatsApp, game marketing, general marketing, google shopping, and ransomware.  Other Macs used for only “in-house” work such as Photoshop have no problem with quitting SONOS.  Given the verbiage in the SONOS privacy documentation I believe this is the issue.

Wouldn’t surprise me. Sonos used to be pretty clear about the fact that they don’t function on VPN networks, although I can no longer find that listed on an FAQ.