Featured Image uploaded, attached and set but only appearing in the media library

I am using the function in this answer to upload, attach and then [set_the_post_tumbnail][2]/featured image to a post which I am creating from an RSS feed.

I ran a test and the output is showing that the attachment ID matches my thumbnail ID. I checked in the media library and it is assigning the correct IDs according to get_post_thumbnail_id but the problem is my featured image meta box is not displaying the image through the dashboard or when using [get the post thumbnail][4] in my template.

Am I missing any steps here? The code is mostly from the answer linked above with a few tests on the end.

global $wp_query;
                wp_insert_post($my_post); // create a new post
                $post_id = $wp_query->post->ID;  // get the ID for the new post


                $image_url = $thumbnail;
                $upload_dir = wp_upload_dir();
                $image_data = file_get_contents($image_url);
                $filename = basename($image_url);
                if(wp_mkdir_p($upload_dir['path']))
                    $file = $upload_dir['path'] . '/' . $filename;
                else
                    $file = $upload_dir['basedir'] . '/' . $filename;
                file_put_contents($file, $image_data);

                $wp_filetype = wp_check_filetype($filename, null );
                $attachment = array(
                    'post_mime_type' => $wp_filetype['type'],
                    'post_title' => sanitize_file_name($filename),
                    'post_content' => '',
                    'post_status' => 'inherit'
                );
                $attach_id = wp_insert_attachment( $attachment, $file, $post_id );
                require_once(ABSPATH . 'wp-admin/includes/image.php');
                $attach_data = wp_generate_attachment_metadata( $attach_id, $file );
                wp_update_attachment_metadata( $attach_id, $attach_data );

                set_post_thumbnail( $post_id, $attach_id );
                echo "Attachment ID: " . $attach_id;
                $post_thumbnail_id = get_post_thumbnail_id( $post_id );             
                echo "Thumbnail ID: " . $post_thumbnail_id; 
                get_the_post_thumbnail($post_id, 'full');