Single File Upload will not attach on form edit

I have single file upload fields that a file is uploaded on the original form submission. When a user goes back in and edits a form, it still shows the uploaded files on the form. When they click update at the end, it sends a notification which attaches the pdf to the notification. The uploaded files do not show in the pdf that is attached to the notification email. If I go in view the form on the back end of WordPress and resend the notification, now the files are attached.