Shortcode Hook returning empty

Hey,

I'm using a generatepress Custom Hook as a shortcode using this function:

function customFunc($atts, $content = null) {
      ob_start();
      do_action('customHook');
      return ob_get_clean();
}
add_shortcode('myShortcode', 'customFunc');

This shortcode works OK in my pages but it is returning empty when I try to save its value into a variable in Ad Inserter:

$code = do_shortcode('[myShortcode]');

That means $code is always empty even if the shortcode works ok in my posts. Why is this happening?