Not all music from iTunes not dragging to Rekordbox

Hi - hope you're well

(just copying this post from somewhere else as it's well written and I have exactly the same problem!)
For some reason, only some of my tracks are moving into Rekordbox when I try and drag in from iTunes.

I have all my music sorted into Playlists in iTunes, so I just want to mirror those in Rekordbox so I can group them into folders (which you obviously can't do using the direct iTunes sync in Rekordbox).

So say I have 100 tracks in an iTunes playlist; I click and drag them into Rekordbox; but only 10-15 will actually move.  No obvious difference between the tracks - all same format, all downloaded, all in the same place on my hard-drive etc..

And it to make it even more confusing, if I go and mind the track in 'Finder' on my Mac (same location that iTunes thinks it is), I can drag it into Rekordbox from there no problem.  But clearly want to avoid having to go track-by-track!

Any help or advice would be amazing! I am using the 'framework' setting in Rekordbox.