How do I delete rogue music folders on music.apple.com and Sonos that are not in the Music app?

and annoyingly, I cannot delete them, from the web interface. I have problems with library non-syncing and this could be the reason. Anyone else seen these or know how to reset them? I have deleted 40,000 songs from my library on Apples recommendation to get back to a basic empty library, and then started building my library again - from scratch (I know, I know). But this could be the issue.

[Re-Titled by Moderator]