Why is the Page Title missing on Pages added with add_submenu_page?

It is a valid question and an issue I have encountered as well.

I did not go through the WP core code to see why the title is missing, but I can offer a solution using the admin_title filter, for people facing a similar problem:

function fix_your_page_title( $admin_title, $title ) {
    if ( get_current_screen()->id === 'your_page_id' && $title === '' ) {
        $admin_title="Your page title" . $admin_title;
    }    

    return $admin_title;
}

add_filter( 'admin_title', 'fix_your_page_title', 10, 2 );

tech