Comment form issue (No explanation for each input) is fixed.
In conclusion, it is just a bug of the theme(Arjuna X 1.6.7).

Fixed details.

Target File: ‘wp-content/themes/arjuna-x/templates/comments/reply-form-advanced.php’

  Wrong: <?php esc_attr(…
  Correct: <?php echo esc_attr(…

There are 7 same mistakes…