Categories of custom taxonomy don’t show any posts

you will need to modify the query on taxonomy term pages to get your post type

try:

add_filter('pre_get_posts', 'filter_custom_taxonomy_posts');
function filter_custom_taxonomy_posts($query) {
    if (is_tax('Your_Taxonomy_Name')) {
        $query->set('post_type', 'portfolio');
        $query->set('posts_per_page', -1);
    }
  return $query;
}