No redirection after form submit

I have setup my contact form in order to track a conversion after filling in the form.
The user should be redirected to a confirmation page. Actually it is not working anymore.

Page: https://valere-klinik.de/informationen/kontakt-burnout-klinik/

Therefore I put in the following snippet in additional settings:
on_sent_ok: “location = ‘https://valere-klinik.de/informationen/vielen-dank/’;”

After the Update to WordPress 4.6.1 this is not working anymore. The support of the Theme developer said that this should be related to any plugin but indeed it is not as I deactivated all of them and tested again.

My Theme is Total 3.5.3
Contact form version 4.5.1