When used with rekordbox, music files that can play in Performance mode won't play in Export mode.

When the XDJ-RX3 is used with rekordbox, the file formats that can be played differ depending on rekordbox modes.

For example, ALAC and high-resolution files can play only in Performance mode.
*In Performance mode, rekordbox loads and plays music. Therefore, you can play only files in formats that rekordbox supports.

For the file formats supported in Export mode, see [Supported file formats] in [Before you start] in the Operating Instructions.
You can read the Operating Instructions [here].

For the file formats supported in Performance mode, see [Music files that can be loaded and played (file formats)] in the rekordbox Operating Instructions.
You can read the rekordbox Operating Instructions [rekordbox.com].