Wordpress Plugin Boilerplate & Submenu Priority - php

Question

I wanted to create a submenu but setting the priority to 11 doesn't seem to work.
I have this on my class-plugin-name.php >> define_admin_hooks()
$plugin_admin = new Plugin_Name_Admin( $this->get_plugin_name(), $this->get_version() );
$this->loader->add_action( 'admin_menu' , $plugin_admin, 'make_menu' );
And on my Plugin_Name_Admin class, I've got:
public function make_menu() {
add_submenu_page('wp-plugin-name', 'Test', 'Test', 'manage_options', 'wp-plugin-name-test', array($this, 'test_page') );
}
public function safe_page() {
echo "test";
}
My problem is that the submenu item shows up but gives me an Insufficient Permissions wp_die(); error.
Now I did a lot of google search and I found out you need to put 11 on the priority instead of 10 like so:
$this->loader->add_action( 'admin_menu' , $plugin_admin, 'make_menu', 11 );
But it doesn't work and the submenu item won't show up instead. I tried putting everything on the wo-plugin-name.php on the root file and just placed simple:
add_action('admin_menu', 'wp_backitup_safemenu', 11 );
function wp_backitup_safemenu() {
add_submenu_page('wp-plugin-name', 'Test', 'Test', 'manage_options', 'manage_options', 'wp_plugin_name_menu_content' );
}
function wp_plugin_name_menu_content() {
echo '<h1>FOO</h1>';
}
And it works like a charm. So what did I do wrong? or is this a boiler plate loader problem?