In Native Instruments Traktor 4, my history playlist is empty after restarting the application.

The following article is from Native Instruments knowledge base:

TRAKTOR’s History Playlist keeps a record of each track played during a TRAKTOR session. You can view it during the ongoing session by selecting the History Playlist icon.

Every time TRAKTOR closes, the software automatically saves the last History Playlist and names it after the current date and time. If your History Playlist is empty after restarting TRAKTOR and you wish to review its content, you will find it in the dedicated Archive folder. This is a subfolder of theExplorer node. The playlists in the Archive are sorted from oldest to newest in descending order.

Within the Archive, you can view and play the contents of the History playlists. If you wish to restore tracks that you had already deleted from your Track Collection, they may still be found in the History playlists. To import the contents of a History Playlist, right-click on it and choose Import to Collection. Alternatively, you can choose Import to Playlists to keep the same Playlist in your Track Collection. You will be able to rename your History playlist and afterwards, it will be added to yourPlaylists folder.

Please note that during a TRAKTOR session a track that is currently playing on a Deck will only be appended to the History Playlist if the following conditions apply:

• The track is playing on air via the speakers (internal mixing mode)
• The track has been playing in the Deck for longer than defined as minimum Play Count(Preferences > Transport >Min. Playtime). For the example below, a track must be playing on the Deck for at least 5 seconds before it is appended to the History Playlist.
  

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