Hey @dermot41! If you have double opt-in41 enabled on your forms, please note that new subscribers will initially come in as 'Unconfirmed' until they click the confirmation button in the incentive email. You can view your unconfirmed subscribers by selecting it from the dropdown at the top of the list on the subscribers page42.
If that doesn't explain it, please reach out to our team at email@example.com (or via the in-app messenger in your account) with a description of this issue and the URL of your landing page so we can test it out. One of our Product Specialists will be able to help troubleshoot further! :)