A person may have registered online, but the confirmation email was sent to the Primary Email. Instead of sending to the email they registered with, it was sent to the Primary Email listed on their constituent record.
We are currently evaluating this issue and will update this article when we have more information.
Steps to Duplicate
From Web > Click User Registration Settings
Copy and Paste the Registration Link into a new tab in your browser
Enter the following information on the form and ensure that it matches an existing constituent record in the database
Enter a new email address on the form
Enter and Confirm the Password
See that the validation email sent to the Primary Email Address on that Constituent's record and not the email address entered when registering