Form submissions not going through?

We are currently running a video-series campaign with a "subscribe" form where visitors who sign up, will receive an email once a new episode is released. I heard from multiple people that they had signed up but have not received anything.

After taking a look at the Subscribe segment I created in Eloqua, it shows there are 240 contacts to date who have filled out the form at least once in the last 12 months. But when I go to the actual form and export the submissions, we have over 600 unique submissions. Any idea what could be causing the submissions to not go through?!?