Bug blocks the displaying of minicart in single product

I have an ecommerce with this plugin installed. It works but gives also a bug, it blocks the displaying of mini cart in the single product page. See here: https://fratellicarbone.it/prodotto/quattro-lattine-da-5-litri/

I studied the plugin code and I found a function which could cause the issue. That’s the function:

add_filter( 'woocommerce_is_checkout', [ $this, 'woocommerce_is_checkout' ] ); //in the __construct()

/**
 * Fake woocommerce checkout page.
 *
 * @param bool $is_checkout Is checkout page?.
 *
 * @return bool
 */
public function woocommerce_is_checkout( $is_checkout ) {
    if ( is_product() ) {
        return true;
    }

    return $is_checkout;
}

If I deregister it, the plugin seems work fine and also the minicart starts again to work. So Anyone can tell me more about this function? I can’t find on google any useful info about the woocommerce_is_checkout filter, and I can’t figure out why this function would block the mini cart.

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