When a form hangs at submit, there may be a Nonce issue.  Especially if the form is large or multi-page.

If you inspect, the console error will look similar to:

If you click on VM163:1 or go to the SOURCES tab you will see: 

Nonce expired, please refresh the page.  If the error persists please contact the site administrator

This should solve the issue:

 If your forms include multiple pages and have a lot of fields in them you may need to increase your max_input_vars to at least 3000 in your PHP.ini and/or wp-config.php settings to prevent a "nonce expired" error or receiving only part of the form during submission.