I have a feeling that your unsubscribe landing page has been designed to unsubscribe the profile from a particular service. It doesn’t impact the “blacklist” fields of profile resource.
Then there is some custom process on yoru side which sets the “do not contact” field with the business logic implemented.
That is why this workflow again did set the “do not contact” information to Yes.
Can you please investigate accordingly or open a support case to assist with the investigation.
Regards,
Vipul