Hello Wayne,
Thank you for the provided details.
According to the screenshots, you have the email notifications being sent in the same Scheduled Task that imports new user accounts. As the task is configured for Organizational Unit object type, the manager email is taken from the manager of the OU, not from the new user. As long as OUs do not have the Manager property, value reference %adm-ManagerEmail% resolves into an empty value. To remedy the issue, you need to move the actions that send the notifications from your Scheduled Task to the Business Rule triggering After Creating a User.