Party Contacts entity/form allows duplication in the same purpose and type. This means you can have the same phone number entered twice in the same contact or the same email address twice. The system does not error or warn user on the duplicate entry. This shouldn't be a problem except for the Export to BYOD (Azure SQL DB) errors out then complaining about this duplicate. The only solution, as customer, is see the job in error, delete the duplication and relaunch the job. MS has confirmed this is the expected behavior and Dev will consider customer votes on this idea. The internal MS reference is: 328675