manuel75

Then on top of the above, when a Doc is set to Private, there’s no way to add a section (it disappears from the Doc Parent list for Admins and Editors as well). ? This is kind of a deal-breaker I have to say, too bad for such an amazing tool otherwise.

Long story short: Private posts are important (they provide editorial management flexibility) and Admins and Editors should have access to and see all Private posts, across the board.

I think I have found a more reliable and straightforward approach. Copy and paste this code inside your theme functions.php:

function walled_garden() {
if( ! is_user_logged_in() )
wp_redirect( '/wp-login.php' );
}
add_action( 'get_header', 'walled_garden' );

I Got it from : https://davidwalsh.name/wordpress-force-login (see the comments).
I think its far better to have a User Login approach to handle this, and avoid plugins that might, as it did happen to me, allow hack and malware contamination when it’s buggy.