Loader spins forever

Hello,

I have a big form on my site, containing a lot of fields.
The form is working great : when you click on submit, the information is sent by mail and everything is ok, except that the loader keeps on spinning forever and never stops. So the sender seems something went wrong and click again.

What happens is that I receive each submission several times… And the user never gets the “form successfully sent” message.

I thought it was an issue with on of the fields so i deleted them one by one.
Now I’m on the development site and there’s only one simple text field remaining.

However the problem remains…

Could you please help me ?

Thanks a lot.
Regards,

The page I need help with: [log in to see the link]