Found it. I was using this code in my functions.php:
$showID = $wpdb->get_var( $wpdb->prepare( "
SELECT ID
FROM $wpdb->posts
WHERE post_name = %s
AND post_type= %s", 'show', 'page' ) );
if ( !$showID ) {
$showID = wp_insert_post( array(
'post_name' => 'show',
'post_title' => 'Show',
'post_type' => 'page',
'post_status' => 'publish'
));
}
wp_update_post( array(
'ID' => $showID,
'post_status' => 'private'
) );
Turns out the wp_update_post with just the ID and post_status makes this issue alive. Even though it has the correct ID to the page.
Did a fresh WordPress install, restored database and fresh installed ACF Pro. This issue still remains. Will now try with a fresh install and import of the custom post types