Check for alarms, that would be the first culprit that comes to mind.  If there aren’t any, within ten minutes of the music paying, submit a diagnostic, then contact Sonos support with the reference number.  They can tell you the source of the music. 

There have been issues for Spotify users, I believe. If a friend connects to your speakers, their access remains until it’s “broken” by you streaming from a different source (or something like that).