Can you post the share link at the bottom of your schema? I’ve set up something similar here and I don’t get duplicates, so I must be doing something differently:
It looks like Mockaroo always generates full name based on the previous first and last name fields. That functionality goes back a long ways and probably isn’t needed anymore given that you can do the same thing with Formulas. I’ll consider removing it. In the meantime you could force it to generate a new name by adding new First Name and Last Name fields for the alias and switching the full name field to a Formula with value alias_first_name + ’ ’ + alias_last_name. If you want to hide the first and last name fields from the output you can do so by naming them starting with two underscores, for example “__alias_first_name”