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As for the drives, they may all be identical on the outside but could have different guts; if the ones that don't work with the XDJ and CDJ-900 are USB3.1 (not 3.0) that's the most likely reason; a different memory manager chipset which is not compatible.
Unfortunately we're not able to guarantee compatibility with all USB drives for all of our products due to the variation of USB drives and specifications, and there are too many models out there to test and certify.