CMB2 metabox with custom after_group_row callback

product-room.php

/**
 * CMB2 Metabox Registration: Product Rooms
 */
function register_product_room_metabox()
{
    $prefix = 'product_';

    for ($idx = 0; $idx < 14; $idx++) {
        $product_rooms_box = new_cmb2_box([
            'id'           => $prefix . 'rooms_box_'.$idx,
            'title'        => rooms_box_title($idx, 'Rooms'),
            'object_types' => ['product'],
            'context'      => 'normal',
            'priority'     => 'high',
            'classes'      => 'cmb2-product-rooms',
            'iterator'     => $idx, // used by variations_box_show_on_cb function
            'show_on_cb'   => 'variations_box_show_on_cb',
            ]);

        // rooms, repeatable group
        $product_rooms_lines = $product_rooms_box->add_field([
            'id'          => $prefix . 'rooms_'.$idx,
            'type'        => 'group',
            'description' => product_rooms_description(),
            'repeatable'  => true,
            'options'     => [
                'group_title'   => __('Room {#}', 'moad'),
                'add_button'    => __('Add Another Entry', 'moad'),
                'remove_button' => __('Remove Entry', 'moad'),
                'sortable'      => true,
                'closed'        => true, // true to have the groups closed by default
            ],
            # This is our custom callback function for outputting dynamic HTML
            'after_group_row' => 'rooms_after_group_row',
            ]);
        
        $product_room_id = $product_rooms_box->add_group_field($product_rooms_lines, [
            'id'   => $prefix . 'room_id',
            'name' => __('Room ID', 'moad'),
            'desc' => esc_html__('eg, &quot;room5&quot;', 'moad'),
            'type' => 'text_small',
            ]);

        $product_room_supplement = $product_rooms_box->add_group_field($product_rooms_lines, [
            'id'   => $prefix . 'room_supplement',
            'name' => __('Room Supplement', 'moad'),
            'desc' => esc_html__('$ Per Room', 'moad'),
            'type' => 'text_money',
            ])
    }
  }
        
/**
  * CMB2 Custom display callback
  */
function rooms_after_group_row($field_args, $field)
{

    /**
      * The 'unset_param_callback_cache()' function, taken from the CMB2.php plugin definition, does nothing here.
      * Probably needs to be invoked earlier, but where?
      */
    $field->unset_param_callback_cache('after_group_row');

    if (!empty($field->value[$field->index])) {
        echo '<div class="cmb-row">';

        echo '<div class="product-rooms-summary  col-md-12">';
        if (!empty($field->value[$field->index]['product_room_supplement'])) {
            # Here we want to output the fresh value - getting cached value instead
            echo " <b>Room Supplement:</b> $".intval(preg_replace("/[^\-.0-9]/","",$field->value[$field->index]['product_room_supplement']));
        }

        if (!empty($field->value[$field->index]['product_room_id'])) {
            # Here we want to output the fresh value - getting the cached value instead
            echo " <b>Room ID:</b> ".($field->value[$field->index]['product_room_id']);
        }

        echo "</div>\n";
        echo "</div>\n";
    }
}