Make Woocommerce breadcrumbs show up using functions.php file

Does your single-product.php contain this?

<?php
    /**
     * woocommerce_before_main_content hook.
     *
     * @hooked woocommerce_output_content_wrapper - 10 (outputs opening divs for the content)
     * @hooked woocommerce_breadcrumb - 20
     */
    do_action( 'woocommerce_before_main_content' );
?>