Problem saving cue points to USB on player (not using rekordbox)

Im trying to save my cue points on the cdj900 unit (not using rekordbox) to a fat32 USB stick from tracks played off CD, sometimes it works fine, but other times when i reload the cd again the cue points are gone. Ive not been able to identify anything im doing differently when it works to when it doesnt. this has been bugging me for ages now! please help.