Official comment
@cassine > Disconnect your XDJ-RX from USB. Open the Audio MIDI Setup application, open the MIDI Studio window, click the drop-down at the top and select New Configuration... then give it a name, and then put the RX in MIDI mode and connect the USB. If it doesn't appear, there may be an issue with the USB cable, or the USB port on the computer - try another of each. If neither of those work, the problem could be with the XDJ-RX itself, but try with another computer to rule that out.
