One Player, Or All Of Them?

Is the drive actually broken?

First, the thing that looks like a failed export and is not one. A drive can be perfectly good and still show nothing, if the player wants a library version your rekordbox did not write. Nothing is broken and none of your music is gone. Ten seconds here saves you deleting playlists you did not need to.

• Try the drive in a different player, if there is one. Reads there but not on the other one, and the drive is fine: it is the library version.
• On a CDJ-3000X, CDJ-1500X, OPUS-QUAD, OMNIS-DUO, XDJ-AZ or XDJ-AN, this is the documented fix. Open the drive in rekordbox, find it under Devices in the media browser, right-click OneLibrary and choose Convert from Device Library. AlphaTheta's one caution: if the drive already holds a OneLibrary, it is overwritten, and any playlist or play history kept only there is lost.
• No OneLibrary entry there? Your rekordbox is too old to write one. Help menu, rekordbox update manager, update, then look again.
• Wait for it to finish, then eject with the eject button in rekordbox, never by pulling the drive.

A recent enough rekordbox writes both library versions in one export, which is why this stops happening once you update. What the split is, after the gig.

Is that what was wrong?

You follow these steps at your own risk. Full disclaimer.