Empty submission fields

We have received 2 empty submissions.  This is concerning because we are using a facebook ad campaign with website conversions as the objective.  

We have 33 submissions with 2 empty submissions.  Please advise.

I see the email field of the jotform is not required:

Please go to the edit mode of your jotform, and do a right click on the field, you will see the Required button:

In this way, you can avoid empty submissions. If you need anything else, please open a new thread, we will be glad to assist you.