orderby
will not contain the title of the column that is being clicked on, but its ID. Change your pre_get_posts
filter to
function my_organization_orderby( $query ) {
if( ! is_admin() )
return;
$orderby = $query->get( 'orderby');
if( 'profile_updated_on' == $orderby ) {
$query->set('meta_key','profile_updated_on');
$query->set('orderby','meta_value_num');
}
}