CDJ 2000 nxs not loading tracks from SD Card

1) Operating System: Windows 10 (Version 10.0.14393 Build 14393)
2) OS Type: 64bit
3) rekordbox version: 4.3.1 & 4.3.0
8) Is rekordbox crashing at all: No 
8b) If not crashing, are there any error messages: No 
9) Are you able to repeat / reproduce the problem: Yes
9a) If yes, can you do it consistently: Yes
12) Provide as much detail of the issue here:

Something has just started happening since upgrading to 4.3.1, and hasn't been resolved by downgrading to 4.3.0 again.

I sync playlists to SD card (fat32) using Rekordbox, and everything goes across. In explorer I can see the audio tracks on the card as well as all the RB data files and settings files etc.

However, when I put the card into my CDJ's, the card is read, it loads my settings, but no playlists or tracks are read by the CDJ - it is as if the card is empty, even though I know it is not.

I have formatted the card and tried again, uninstalled RB cleared out all the program and data files, reinstalled RB, restored my library from backup - sync'd to SD card but the same thing happens.

Same thing happens on 2 other cards as well and happens on both decks...

Any ideas?