Contact Form submit gets stuck on empty page /challenge#contact_form

Hi!
We have a contact form (created by {% form ‘contact’ %}) which we check upon submitting via a with javascript and if all is ok, we submit the form with javascript.
What then happens is that the page
/challenge#contact_form
is loaded and it is stuck there, the page is empty, nothing is displayed. There is no error in the dev tools console.

Any idea to get this working?