Ok remove the hook and add this PHP Snippet to your site:
add_filter( 'option_generate_secondary_nav_settings','lh_single_posts_secondary_nav_settings' );
function lh_single_posts_secondary_nav_settings( $options ) {
$category = get_the_category();
$category_label = $category[0]->cat_name;
if ( !empty( $category ) ) {
$options['secondary_nav_mobile_label'] = $category_label;
}
return $options;
}