Official comment
It should but with some users, we've found you need to refresh a couple of times (click the reload icon to the right of the iTunes label on the left window), other users have needed to simply wait a couple of minutes.
Engineers are working to improve this behaviour and your patience is appreciated.
Please be aware you can always drag-and-drop playlists into rekordbox manually to re-create them if the sync isn't working properly for you, or you can use the Sync Manager which acts as a one-way sync/import from iTunes.