Ive managed to figure it out, and it is indeed special chars in filenames that was causing the issues.
Freestyle\ -\ �gon\ som\ Glittrarn\ 98.mp3
Me\'Shell\ Ndeg�Ocello\ -\ *
La\ Cream\ -\ Chate�u\ d\'Amour.mp3
and a few others.. but about 9 files in total caused the issue
Yes, the 59 files over SMB, in that MP3s folder, are exactly the same.
And yes, all 59 files seen on the SMB share are also visible on the NFS share of the same folder.
Disk Share for disk2 (MP3s folder) over SMB = 59 files
Disk Share for disk2 (MP3s folder) over NFS = 6375 files
User Share for Music (MP3s folder) over SMB = 59 files
User Share for Music (MP3s folder) over NFS = 6375 files
I started to go through them, but 6000ish files are on 'Disk2'.. basically ~400GB of the 600GB of data. So its not like just those 59 files are on a different disk.
Besides, NFS is working fine.. it has to be some issue with SAMBA.
EDIT: The ENTIRE contents of the 'MP3s' folder, is on disk2.
Just confirmed that my Windows 10 and Windows 11 laptops only see the 59 files that I see on macOS. So its definitely an issue on the unRAID side of things, and its not specific to macOS.
I'm pretty sure I have looked at it with Windows over the years. I will boot into Windows to confirm shortly, and also test with one of my Windows laptops.