wp_insert_attachment returns thumbs with resolution 1px

Hi,
in my plugin I use function wp_insert_attachment. I use it in a standard way like here Those Thumbnails in Media Library which I added this way shows only with resolution 1 px, other thumbnails here shows normally. When I try to edit some of them by view post in Media library I see normal picture. I don’t know what I made wrong. I am sure it workded previously well (probably before update to newer version?). Now I have version 3.8.1 and I tried it on 3 different servers with this version.
My code is:

$attachment = array(
    'post_mime_type' => 'image/jpeg',
    'post_title' => 'pic',
    'post_content' =>'',
    'post_status' => 'publish'
);
$attach_id = wp_insert_attachment( $attachment,$upload_im);
set_post_thumbnail(get_the_ID(),$attach_id);

Any idea to works it?