Issue:

In single-product.php when using the_content(); the woocommerce-product-gallery div have the opacity set to: 0.

Solving:

• use wp_head(); in the header.php and wp_footer(); in the footer.php
• add the following code to functions.php:

add_action( 'after_setup_theme', 'yourtheme_setup' );

    function yourtheme_setup() {
        add_theme_support( 'wc-product-gallery-zoom' );
        add_theme_support( 'wc-product-gallery-lightbox' );
        add_theme_support( 'wc-product-gallery-slider' );
    }

reference: