I am having the same problem. When the form is filled out and the submit button is clicked – it seems nothing happens – the green message “Your message was sent successfully. Thanks.” that usually comes up is not showing – yet the contact info is being emailed. The problem is the user doesn’t realize that the form info was sent and they try multiple times.
It’s strange because I have the exact configuration on other sites and it’s working. Any ideas on how to resolve it? It was working perfectly before on the site in question.