Next time it happens note where the music is coming from. It is probably Spotify, and if it is, it is likely a guest that once used Spotify Direct on your system still has access. Cut their access by playing something non-Spotify on each device. If the source is NOT Spotify, immediately create a diagnostic code and send it to Sonos support, they will be able to tell you what happened.

Do you have TV Autoplay enabled? I’ve had issues with cable boxes updating in the middle of the night, then starting to play. If this is the case you can disable TV Autoplay, make sure that another source is selected, or turn down the Volume for the player. In my area the cable box updates occur at about 3:30am on Wednesday mornings. You may have some success if you disable CEC (or whatever it is called on your TV) on the TV.

No guest uses my system. It’s the speaker in my bedroom and it turned on several times in the middle of the night while I was asleep.

Then the recommendation by controlav is your best bet. So far, there has not been a confirmed case of the software randomly playing anything. The diagnostic information will likely suggest where the command is coming from.