Getting 404 on taxonomy page

I’ve solved this for myself with rewrite rule.

The story: I have "piece" custom post type, taxonomy "media_tag" with "m_audio" term and taxonomy "genre_tag" with "g_sacred", "g_folk" etc. And I want to have an URL like /piece/audio/<genre> to access archives.

So, now I have in my functions.php:

add_filter( 'rewrite_rules_array', 'my_insert_rewrite_rules' );
function my_insert_rewrite_rules( $rules ) {
  $newrules = array();
  // audio pieces with g_sacred tax:
  $newrules['piece/audio/([a-z]+)(/page/([0-9]+))?'] =
      'index.php?post_type=piece&media_tag=m_audio'
      . '&genre_tag=g_$matches[1]&paged=$matches[3]';

  return $newrules + $rules;
}

and nothing in taxonomy-media_tag-m_audio.php template.

Hope this helps.

Also, I have this in my functions.php:

// add_action( 'wp_loaded','my_flush_ALL_rules' );
function my_flush_ALL_rules(){
  global $wp_rewrite;
  $wp_rewrite->flush_rules();
}

And I uncomment add_action for a moment to flush rules after changes.