Dynamic generated dropdown value is not passed to controller after page refresh.

Are you passing back a new csrf hash when your controller responds to the AJAX call? Normally you get an access forbidden error if you don't, but maybe it's buried.

Code:

$ajax_data['csrf_token_name'] = $this->security->get_csrf_token_name();
$ajax_data['csrf_hash'] = $this->security->get_csrf_hash();