When I track the submit in the browser's console... I see that the page is requested in http:// format... That is being blocked as mixed content.
I'm not sure where or how the url is changing to http:// instead of https:// which is what is causing the issue. I'd have to debug this live with FTP access to determine any more.
Maybe try updating line 14 from:
$WAFV_Redirect = "";
$WAFV_Redirect = "https://www.landgame.eu/il-mistero-delle-12-perle/puntata-1/feedback.php";