Soundiiz is available for Beatport LINK and Beatsource LINK offers. However, even if a track is available in Beatport or Beatsource catalog, that doesn't means this same track is available in LINK offer.
The LINK offer is a streaming offer different than the catalog offer on Beatport or Beatsource. Music owners could not have allowed the LINK (streaming) usage of their songs.
That's why some songs could not be matched by Soundiiz while they are available on Beatport or Beatsource.