Problems With USB / Drives Being Recognised Once Ran Throygh RB

I'm having major issues with my USB's not being recognised by (specifically a set of XDJ-1000 mk2) regardless of which version of RB they're sorted through. They all show on my XZ fine wuth the playlists etc., but these specific decks keep saying FORMAT USB. They're all FAT32 and as I say work fine on my XZ and up until last weekend on every other decks I ever plugged them into but last week they also failed on a set of Nexus 2000's. Firmware on machines uo to date and USBs are SanDisk Ultra 128gb. Also it happened with my 2TB sandisk SSD and again as mentioned they work fine in my XZ. Any ideas as it sort of makes me nervous turning uo for gugs and if they all fail I'm screwed!