thumbs are coming with blank id

[bydbest]

Hello,
@nicolqs
we are using this class and its working just fine for main image when we upload through media but not working for thumbs generated by media.

we are hooking like this wp_async for
add_action( 'wp_async_wp_generate_attachment_metadata', array( &$this, 'media_uploader_callback' ) );
add_filter( 'wp_generate_attachment_metadata', array( &$this, 'thumbnails' ) );

I tried adding wp_async to add_filter but then nothing is coming to remote server. so is there any way? as main image works fine with first hook

i can see with var_dump that full data is available including thumbs but only main image are going to remote server and checked with file put contents and i can see that thumbs are not coming as thumbs id were empty