Drupal View of CiviMember troubleshooting
Is there nothing to give you a clue in the actual table of results? Eg are the duplicates ones that have multiple websites (since that field has not filtering in field for ' website type' afaik but you should be able to apply a Views Filter)
That seems the most likely reason.
If not, have you tried setting the Query Settings (under Advanced) to Disinct or Pure Distinct.
If none of that helps, can you attach the view?