get_post_meta() returns an empty string - php

Question

I created a function, which duplicate products for specific users, when another user submit a post form.
In general I don't have issues to duplicate the products. When user ID 151 submit the post form, the product is duplicated for the other two users in the array under variable $relatedVendors. However, I have one issue within the function. As you can see I take the wpuf form ID from the original product and would like to store this id also for the other duplicated products (posts). For this case I use get_post_meta for the original post and then add_post_meta for the duplicated posts in the foreach loop. Now my issue is, that the meta key is populated for the duplicated posts, but the wpuf ID is not in the value field.
I tried to figure out, what the issue is. So the add_post_meta seems to work, because in one run I have hard coded an integer instead of $wpuf variable. In this case the hard coded id was stored in the meta value field. The same works fine for the second add post value "catalog".
For me it looks like that the get_post_meta is not working. I moved this part right below get the user id, then within the if state and within the foreach loop. I changed the priority as well. So, know I'm asking for help, why the get post is not working.
add_action('save_post', 'myWoo_duplicatePost', 10, 2);
function myWoo_duplicatePost($postID, $post) {
$current_user = wp_get_current_user();
if (isset($post->post_type) && $post->post_type == 'product' && $post->post_modified_gmt == $post->post_date_gmt && $current_user->ID == 151 ) {
$relatedVendors = array(114,88);
if ($post != null) {
remove_action('save_post', 'myWoo_duplicatePost', 10, 2);
foreach ($relatedVendors as $vendor) {
$args = array(
'comment_status' => $post->comment_status,
'ping_status' => $post->ping_status,
'post_author' => $vendor,
'post_content' => $post->post_content,
'post_excerpt' => $post->post_excerpt,
'post_name' => $post->post_name,
'post_parent' => $post->post_parent,
'post_password' => $post->post_password,
'post_status' => 'publish',
'post_title' => $post->post_title,
'post_type' => $post->post_type,
'to_ping' => $post->to_ping,
'menu_order' => $post->menu_order
);
$new_post_id = wp_insert_post( $args );
$wpufID = get_post_meta($post_id, '_wpuf_form_id', true );
add_post_meta( $new_post_id, '_wpuf_form_id', $wpufID );
add_post_meta( $new_post_id, '_visibility', 'catalog' );
}
}
add_action('save_post', 'myWoo_duplicatePost', 10, 2);
}
}