Without a doubt, the solution presented in
https://github.com/osTicket/osTicket/pull/5694/files
It works only that it has a little bug
The solution says:
$field_list = array('response', 'note', 'answer', 'body',
'message', 'issue', 'description');
$tfield, 'issue', $afield);
I solved it with:
$field_list = array('response', 'note', 'answer', 'body',
'message', 'issue', 'description',
$tfield, 'issue', $afield);