Is it possible you haven't re-analysed / re-exported the tracks in rekordbox since the CDJ-2000nexus was released? Previous tracks would have been without the enhanced waveform, but you should still have the standard data for track name, artist, genre, BPM, key, etc.
Oh, and the rekordbox button on the 2000nexus is only for connecting to a computer or wireless device running the rekordbox app, not USB devices.