Using a custom REST API in WooCommerce, the data from do_actions in content-product.php do not generate any output. Why?

Question

I have WooCommerce v3.5.6 installed, and the code works as expected.

But, if updated to any subsequent versions, all these do_action statements have no output over the REST API.

do_action( 'woocommerce_before_shop_loop_item' );

do_action( 'woocommerce_before_shop_loop_item_title' );

do_action( 'woocommerce_shop_loop_item_title' );

do_action( 'woocommerce_after_shop_loop_item_title' );

do_action( 'woocommerce_after_shop_loop_item' );

This is how I fetch and transfer the product HTML data (sale, wishlist, image, title, price, add to cart link) that those do_action statements output.

$this->output .= wc_get_template_part('content', 'product');

What's wrong? Please assist.