Clonable select_advanced with ajax

Hi, we need to be able to link a post to one or more other posts so we used metabox.io to create a group of clonable fields with a type of "post" to do this. However, since we have a few thousand posts, the performance was really poor once a user had associated a few posts (sometimes they associate as many as 30+).

No we are hoping to make the field a "select_advanced" field and performance ajax lookups instead to avoid these performance issues. We did this by creating a simple wp_ajax endpoint that returned the matching posts in json as select2 expects and that almost works. The select_advanced dropdown renders properly and the ajax search works returning results but clicking on a result does nothing.

Shouldn't this work?

Following is our metabox group definition:

$meta_boxes[] = array(
    'id' => "finite_scroll",
    'title' => __('Finite Scroll'),
    'post_types' => array('recipe'),
    'fields' => array(
        array(
            'id' => $prefix . 'related_recipe',
            'type' => 'group',
            'clone' => true,
            'sort_clone' =>true,
            'fields' => array(
                array(
                    'name' => __('Related Recipe:'),
                    'id' => $prefix . 'rel_recipe',
                    'type' => 'select_advanced',
                    'options' => array('' => ''),
                    'js_options' => array (
                        'ajax' => array(
                            'url' => '/wp-admin/admin-ajax.php?action=select_advanced_post_lookup&post_type=recipe',
                            'dataType' => 'json',
                            'type' => 'get',
                            'delay' => '250'
                        ),
                        'minimumInputLength' => 3,
                        'allowClear' => true, 
                        'placeholder' => 'Select recipe'
                    ) 
                )
            )
        )
    )
);

Here is the wp_ajax function that sends search results to select2:

add_action('wp_ajax_select_advanced_post_lookup', 'select_advanced_post_lookup');
function select_advanced_post_lookup() {
    global $wpdb;
    $post_types = "'".implode("','", explode(',', $_GET['post_type']))."'";
    $keyword = "%".$wpdb->esc_like($_GET['q'])."%"; 

    $sql = "SELECT ID, post_title".
        " FROM $wpdb->posts".
        " WHERE post_title LIKE '". $keyword . "'" .
        " AND post_type IN (". $post_types .")" .
        " AND post_status='publish' ".
        " ORDER BY post_title LIMIT 0,15;";
    $results = $wpdb->get_results($sql);
    $response = array(
        'results' => array()
    );
    foreach ( $results as $result ) {
        $response['results'][] = array( 'id:' => $result->ID, 'text' => $result->post_title );
    }
    wp_send_json($response);
}