Hi @nigelsmith
Are you still having this problem?
Until the advent of the “iTunes app” becoming the “Music” app, playlists were stored as a file called “"iTunes Music Library.xml" or “iTunes Library.xml” in the parent folder. The “Music" app no longer creates this file. As Sonos speakers try to import the playlists from the xml file which “Music" no longer creates, when you now index music the Sonos App first reads the “Music" app’s playlists (from where ever they are now stored) and writes the xml file in the shared folder so that when the speaker accesses the folder via network, it can find that xml file and import the playlists on it. This happens because the speakers cannot access the new location of where those playlists are stored via the network share.
Removing this file can often fix problems with missing/extra/out-of-date playlists, but we recommend you rename the file instead of deleting it, in case you need to back-track. Once you do that, reindex from the Sonos app.
There’s more detail on this other thread: