WordPress php filter admin_body_class not working

About your issue in admin body class, WP Codex documentation admin_body_class, class as string ( not array ), there are some of your function like get_saved_network_option not returning true that cause $new_classes not setted in array.

This code correct, we need return in string, but $new_classes maybe in string empty or not array.

return $body_classes . ' ' . implode( ' ', $new_classes ) . ' ';

For login page class, you are correct to set login_body_class in array, BUT you set condition too early as @Bruno Cantuaria comment, take a look your code:

// Only when logged in
if ( ! is_user_logged_in() ) {
    return $body_classes;
}

So thats why you class settings not return, it only work if user not logged-in. I hope this helps.