the plugin ‘Visual Composer’ is the same plugin than ‘WPBakery Page Builder’. The name changed. You can check that in the plugin website: https://codecanyon.net/item/visual-composer-page-builder-for-wordpress/242431
I have modified the plugin options to allow custom portfolio post. In the page ‘WPBakery Page Builder Settings > Role Manager’, I have changed the first option ‘Post types’. I have created a new post called ‘Custom post’ to check if it works fine. And so it is. The post has private visibility 😉
About the error in the file loop.php, I know the solution but I couldn’t edit the file to resolve it. I have sent you the file modified to your email. Could you upload it via FTP please? You have to replace it in theme folder.