Hi,
I have resolved the issue. I have edited single-portfolio.php.
Find this code:-
$thumb_img_url = wp_get_attachment_url( $thumb_image, 'full' );
Change to:-
$thumb_img_url = wp_get_attachment_url( $thumb_image, 'full' );
$thumb_img_url = wp_get_attachment_url( get_post_thumbnail_id($post->ID),'full' );
Thanks ๐
With Best Regards
Mohammad