Official comment
If you are not exporting from rekordbox directly to the USB, that's why you have no waveform view on the XDJ-RX. If the EXPORT option is not available, it could be the USB device is not prepared in a format supported by rekordbox; please use FAT32 or HFS+ (with Master Boot Record) to format your USB drive and be sure that rekordbox is in EXPORT mode, not PERFORMANCE mode.