Show subcategories broken when WP/WC updates


I’ve been given to mantain a site who wasn’t updated for a while: it had WP 4.9.15 and WooCommerce 2.6.14

Now I’ve made a site test where i’ve updated all these things and now i have WP 5.4.2 and WC 4.3.1

One thing that is broken and i’m not able to figure why is the page showing the products by category: they have a 3 level category tree. It worked this way: if the category asked was a leaf, the page showed the product list. If it wasn’t a leaf, it showed all the subcategories.

The template page doing this is archive-product.php which has this simple loop to show everything:

            <h1 class="page-title"><?php woocommerce_page_title(); ?></h1>              <?php if ( have_posts() ) : ?>                  <?php                     /**                      * woocommerce_before_shop_loop hook                      *                      * @hooked woocommerce_result_count - 20                      * @hooked woocommerce_catalog_ordering - 30                      */                     do_action( 'woocommerce_before_shop_loop' );                 ?>                  <?php woocommerce_product_loop_start(); ?>                      <?php woocommerce_product_subcategories(); ?>                      <?php while ( have_posts() ) : the_post(); ?>                          <?php wc_get_template_part( 'content', 'product' ); ?>                      <?php endwhile; // end of the loop. ?>                  <?php woocommerce_product_loop_end(); ?>                  <?php                     /**                      * woocommerce_after_shop_loop hook                      *                      * @hooked woocommerce_pagination - 10                      */                     do_action( 'woocommerce_after_shop_loop' );                 ?>              <?php elseif ( ! woocommerce_product_subcategories( array( 'before' => woocommerce_product_loop_start( false ), 'after' => woocommerce_product_loop_end( false ) ) ) ) : ?>                  <?php wc_get_template( 'loop/no-products-found.php' ); ?>              <?php endif; ?> 

Now this page works only if the category requested is a leaf thus it has to display a list of products. If the category requested is not a leaf, no subcategory is shown and the page is blank with only the category name (page_title) showing. So it means that the query is somewhat did good, but why no category is shown? Thank you if you can help me solving this trouble