function change_frontend_editor_iframe_url($url) {
return str_replace("http://", "https://", $url);
}
add_filter('vc_frontend_editor_iframe_url', 'change_frontend_editor_iframe_url');
Snippets: Switch Visual Composer Front End Editor HTTPS Protocol
All PHP snippets should be added via a child theme's functions.php file or via the Code Snippets Plugin (or alternative plugin)