Use this:
$next_in_line = get_post_meta(esc_attr($product->get_id()), '_next_in_line', true);
print_r($next_in_line['user_id']);
print_r($next_in_line['product_id']);
Let me know if works.
Use this:
$next_in_line = get_post_meta(esc_attr($product->get_id()), '_next_in_line', true);
print_r($next_in_line['user_id']);
print_r($next_in_line['product_id']);
Let me know if works.