ERR_NAME_NOT_RESOLVED in the console

[lucrus73]

I've added a custom field to my CPT using CMB2 and this code:

$cmb->add_field( array(
	'name'    => __( 'Place', 'my-plugin-slug' ),
	'desc'    => __( 'The place where this playlist is going to be used', 'my-plugin-slug' ),
	'id'      => VBCPLM_Playlist_MetaKeys::$place,
	'type'    => 'custom_attached_posts',
  'options' => array(
    'show_thumbnails' => true, 
    'filter_boxes'    => true, 
    'query_args'      => array(
      'posts_per_page' => 10,
      'post_type'      => 'place_type',
    ), 
  ),
  'on_front'        => false 
));

but when the edit post backend page loads, I get the following in the console:

attached-posts-admin.css:1 Failed to load resource: net::ERR_NAME_NOT_RESOLVED
attached-posts.js:1 Failed to load resource: net::ERR_NAME_NOT_RESOLVED

and the attached posts field doesn't work (the '+' button does nothing).

I'm using the latest CMB2 code, up to date to the latest commit as of now.