Hierarchical taxonomies in permalink cause 404 for sub term archive

Question

I've got a custom post type with hierarchical taxonomies. The permalink structure is as follows:

www.mysite.com/post_type/taxonomy_term -> works (tax archive page)
www.mysite.com/post_type/taxonomy_term/post_name -> works (post page)
www.mysite.com/post_type/taxonomy_term/taxonomy_sub_term -> 404 error (sub tax archive page)
www.mysite.com/post_type/taxonomy_term/taxonomy_sub_term/post_name -> works (post page)

Custom post type function with the important settings (output from CPT UI):

$args = array(
    "has_archive" => true,
    "hierarchical" => false,
    "rewrite" => array( 
         "slug" => "diensten", 
         "with_front" => false 
     ),
    "taxonomies" => array( "dienst_categorie" ),
);

register_post_type( "diensten", $args );

Taxonomy function with the important settings (output from CPT UI):

$args = array(
    "hierarchical" => true,
    "rewrite" => array( 
        'slug' => 'diensten', 
        'with_front' => false,  
        'hierarchical' => true,
    ),
);
register_taxonomy( "dienst_categorie", array( "diensten" ), $args );

With some custom code based on this website I've come to the following code:

function resources_cpt_generating_rule( $wp_rewrite ) {
    $rules = array();

    $post_type_diensten = 'diensten';
    $terms_diensten = get_terms( array(
        'taxonomy' => 'dienst_categorie',
        'hide_empty' => false,
    ) );
    foreach ( $terms_diensten as $term ) {
        if ( $term->parent > 0 ) {
            $pterm = get_term( $term->parent, 'dienst_categorie' );
            // The line below doesn't work as expected.
            $rules[ 'diensten/' . $pterm->slug . '/' . $term->slug . '/?$'  ] = 'index.php?taxonomy=dienst_categorie&term=' . $term->slug;
            $rules[ 'diensten/' . $pterm->slug . '/' . $term->slug . '/([^(/)]*)$' ] = 'index.php?post_type=' . $$post_type_diensten . '&' . $post_type_diensten . '=$matches[1]&name=$matches[1]';
        } else {
            $rules[ 'diensten/' . $term->slug . '/([^/]*)$' ] = 'index.php?post_type=' . $post_type_diensten . '&' . $post_type_diensten . '=$matches[1]&name=$matches[1]';
        }

        // This line works, but is not dynamic.
        $rules[ 'diensten/zonwering/zonweringreparaties/?$' ] = 'index.php?taxonomy=dienst_categorie&term=zonweringreparaties';
    }
}
add_filter( 'generate_rewrite_rules', 'resources_cpt_generating_rule' );

function change_link( $permalink, $post ) {
    if ( 'diensten' === $post->post_type ) {
        $resource_terms = get_the_terms( $post, 'dienst_categorie' );
        if ( ! empty( $resource_terms ) ) {
            foreach ( $resource_terms as $term ) {
                if ( 'featured' === $term->slug ) {
                    continue;
                }

                if ( $term->parent > 0 ) {
                    $pterm = get_term( $term->parent );
                    $permalink = get_home_url() . '/diensten/' . $pterm->slug . '/' . $term->slug . '/' . $post->post_name;
                } else {
                    $permalink = get_home_url() . '/diensten/' . $term->slug . '/' . $post->post_name;
                }
                break;
            }
        }
        return $permalink;
    }
}
add_filter( 'post_type_link', 'change_link', 10, 2 );

Notice the commented lines. One is hardcoded and the other is dynamic, and based on tests in a template the dynamic one puts out the same code as the hardcoded one, but it doesn't work. I suspect this has something to do with the regex patterns, but I'm unable to figure out why.

My question is: what is the correct rewrite rule to be able to access the archive page of a sub term based on the term/subterm url hierarchy?

Answer 1

I've not reviewed your code, just a quick thought:

Have you tried Going to Settings => Permalinks and just clicking 'Save Changes'? That flushes the rewrite cache.