wp_get_nav_menu_items wp-admin/customize.php problem

I was getting the same fatal error after creating a similar dynamic menu. What fixed the issue for me was redefining the default values:

$post->target="";
$post->attr_title="";
$post->description = '';
$post->classes="";
$post->xfn = '';
$post->status="publish";
$post->original_title="";

So your foreach loop would look like this:

foreach ( get_posts( $category_ten_last_posts ) as $post ) {
   $post->menu_item_parent = $item->ID;
   $post->post_type="nav_menu_item";
   $post->object="header-lasts";
   $post->type="header-lasts";
   $post->menu_order = ++$menu_order;
   $post->title = get_the_post_thumbnail( $post->ID ) . ' ' .$post->post_title;
   $post->url = get_permalink( $post->ID );
   $post->target="";
   $post->attr_title="";
   $post->description = '';
   $post->classes="";
   $post->xfn = '';
   $post->status="publish";
   $post->original_title="";
   $child_items[]= $post;
}