Maybe this will help someone, 'cause I've been struggling with the same issue. For me these download slots were occupied by torrents from which I have selected only certain files to be downloaded (eg. from packs, collections).
I am not sure this is intended behavior, but in this case the torrents appear completed in my client and still they are counted as incomplete on the website (see user details page and click on "Show leeching torrents" to see which torrents wrongfully occupy these slots).

Maybe this will help someone, 'cause I've been struggling with the same issue. For me these download slots were occupied by torrents from which I have selected only certain files to be downloaded (eg. from packs, collections).
I am not sure this is intended behavior, but in this case the torrents appear completed in my client and still they are counted as incomplete on the website (see user details page and click on "Show leeching torrents" to see which torrents wrongfully occupy these slots).