Hi,
Thank you for reaching out to us.
Are you referring to the Email Notification sent to the user after the Registration? Do you use the Email Confirmation feature? Did you tried the Registration logged in as Admin?
Did you tried to deactivate all other plugins and use a default WordPress theme? Maybe there is a theme/plugin conflict.
Try to register a user on the Default WordPress Registration form, logged out as Admin, to see if you receive any notification.
Best regards,