The joy (?) of Spotify Connect is that it requires connection to your internet only the first time at setup. Once that’s been done, it maintains a ‘grip’ on the Sonos until such point as the Sonos changes to a non-Spotify stream.

If you’re interested in what command is changing your choice, and by connection, where that command is coming from (including, in the case of Spotify Connect, outside your WiFi), you can 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, they get sensitive about GDPR.

What I’d do, and try to establish as a habit, is to change to some other streaming source first, either at the end of anyone else being at your home, or just before starting this ‘white noise’ stream, to ensure that any pre-existing Spotify Connect setups have been stopped. Then you should be able to play your white noise track without any concerns.

However, if you find that there’s something else going on, please let us know. Since Spotify Connect started, it’s been the reason this kind of thing has been occurring, there have been no other reports of the Sonos system actually failing, and changing things on its own. 

Thanks for your reply. I tried switching streams as you suggested; no dice. But then I tried a similar track on Sonos Radio, and have had no problems. Good enough; looks like a Spotify problem. Thanks!

​@Travesty 

Also maybe check your list of Recently Played on the Spotify app (not on the Sonos app) to look for any songs you didn’t play and ensure no-one else has gained access to your Spotify.