add_filter 'body_class' only working for logged in users

The below code works fine for logged in users but not for non logged in users. How do I make it work regardless of user type?

add_filter( 'body_class', 'custom_body_class' );
function custom_body_class( $classes ) {

  $classes[] = 'guest-author';
  
  return $classes;
}

I have added this code to my functions.php file.