Rokordbox usb stick very slow on cdj900 & cdj2000

Hello guys
I recently Exported my music library from my PC to my Usb 3.0
After testing it on my XDJ1000 ! worked perfectly !
Then i got to work and the dj set is cdj900 + cdj2000
so on both players with different Usbs ! each time i try to enter a playlist it freeze and say please wait , it takes 1 minute at least to enter a playlist so i can load a track
I have one more USB backup ( My library music) not exported from Rekordbox and it worked so fast and great !!

i got back home after work tested my usbs on my XDJ 1000 Again. all is perfect

Any idea what can it be ??

P.S.: My Usb's are formatted Fat32 and i checked everything online ! nothing
any help ??