Taxonomy posts on Archive page

What you are doing

Your foreach is nested inside while (have_posts()) : the_post();. This while loop, loops through each of your posts (in the genre ‘hip_hop’).

So for each post in the genre ‘hip_hop’, you find the post’s taxonomy terms for the taxonomy ‘sub_genre’ (this is the contents of $cam_brands). Then, for each associated term (in $cam_brands) you get all posts associated to that term (or
$brand).

You final foreach loops through each of these posts and displays them.

What I think you are trying to do

I’m not aware of any native and straightforward way WordPress can ‘split’ all the posts of a particular taxonomy term into it’s children. But the following will do that (albeit, not in a particularly efficient way).

Also, it appears ‘sub_genre’ is a separate taxonomy from ‘genre’ – am I right? If you want a parent-child relationship, you should simply make ‘genre’ a hierarchal taxonomy, and create sub-genres in the same way that you create ‘sub-categories’. Once you’ve done that, the following should work with the below caveats.

$term = get_queried_object();

//Get all children of this term;
$children = get_terms( 'genre', 
    array(
        'parent'=>$term->term_id;
    ) ) ;

if($children):
    //We have an array of child (of current genre) terms. Loop through and display the posts
    foreach($children as $child):
        echo '<h2>'.$child->slug.'</h2>';

        // The Query - get all posts for this child-genre.
        $args = array('post_type' => 'track', 'taxonomy' => 'genre', 'term' => $child->slug, 'post_status' => 'publish','posts_per_page' => -1);
        $child_posts = new WP_Query ($args);

        // The Loop - display all posts for this child-genre.
        while ( $child_posts->have_posts() ) : $child_posts->the_post();
            echo '<li>';
                the_title();
            echo '</li>';
        endwhile;

        // Reset Post Data
        wp_reset_postdata();
    endforeach;
else:
    //On genre with no children - you may want to do something else.
    echo 'No sub-genre for this genre found';
endif;

Caveats

• This code isn’t tested 😀 (but should work)
• It relies on your genre/sub-genres all being part of one hierarchal
• Visiting a genre with no children will display the ‘no sub-genre’ message.
• Tracks which have are associated with a genre term, but not any of its children will not be displayed.