It’s possible that the USB sticks encrypt the data, which is bad news for most devices apart from PCs or Macs.
The other likelihood is that the sticks are usb3.
The front USB port on the SC5000 is usb2 only, whilst the rear USB ports are for USB3 sticks.
Some sticks claim a certain anount of usb3/2 backwards compatibility, but that’s often patchy, not just for DJ use but for all sorts of situations.
Give the sticks a try in the usb3 sockets on the rear of the players, if they don’t work there either, I suspect it’s some odd data encryption or some deep “feature” on the USB sticks. When you plug the sticks into a main pc do the sticks create a pop-up splash screen announcing themselves, or show up as more than one drive letter eg: you plug in one stick and get two drive letters (like G and H) appearing on the computer? If so, there’s some odd dual/hidden partition doing odd things.