Why doesn't form submission work in Drupal when adding a file type field?

Question

Drupal

Good afternoon! There is a site on Drupal 7.43, the Webforms 4.12 module is installed. The trouble is that form submission stops working if you add a file type field for uploading pictures. At the same time, the file itself is uploaded to the server - but the message about submitting the form does not appear, there is a redirect to the completed form and that's it. What can be wrong?
An example of a non-working form:
test.fsmoda.com/content/wfcontact-2
An example of a working form without a field of type file:
test.fsmoda.com/en/content/webform-contact-1
PS. It doesn't matter if AJAX is connected as a Webforms AJAX module or not.