Albums deleted from server still show in app

[nfnc]

I just discovered another baffling situation when looking at the sub-folder for the duplicate albums under the "Music" folder in the NAS.

In addition to the tracks for the album, there is a rogue sub-folder (which may be named after a track in the album or be unrelated) with random tracks culled from other albums in the music library. These rogue random tracks do not show up on iTunes or the Lumin/Kinsky apps.

For example, under Music/Pet Shop Boys/Discography/, all the tracks in the album will be listed - all is good. However, under Music/Pet Shop Boys/Discography/So Hard/, there will be random tracks from other albums listed in the "So Hard" sub-folder (which takes its name from a track in the Discography album).

I then trace the tracks to another album in the music library (in this case, Barbra Streisand: Love is the Answer), but there are no tracks missing from the Barbra Streisand album.

This is so odd...