It seems that it indeed comes from the javascript on your website as I suspected.
There is no error, however, if you deactivate the javascript on that page (F12->settings->disable javascript on chrome) it works properly, as it does on our end and on our demo website.
I would guess that it comes from the javascript of your template which interferes with that. If you switch to another template temporarily, that should solve the problem. In that case, please contact your template provider for help on that.