Fatal error: Uncaught Error: Call to a member function get_id()

А если блок кода на этой строчке

foreach ( $attributes as $param ) :
	if ( true === $param['variation'] ) {
		$param_value = $offer->get_attribute( wc_attribute_taxonomy_name_by_id( $param->get_id() ) );
	} else {
		$param_value = $product->get_attribute( wc_attribute_taxonomy_name_by_id( $param->get_id() ) );
	}
	/* @var WC_Product_Attribute $param */
	$yml .= '        <param name="' . wc_attribute_label( wc_attribute_taxonomy_name_by_id( $param->get_id() ) ) . '">' . $param_value . '</param>' . PHP_EOL;
endforeach;

заменить на:

foreach ( $attributes as $param ) :
	if ( self::woo_latest_versions() ) {
		$taxonomy = wc_attribute_taxonomy_name_by_id( $param->get_id() );
	} else {
		$taxonomy = wc_attribute_taxonomy_name_by_id( $param['id'] );
	}

	if ( true === $param['variation'] ) {
		$param_value = $offer->get_attribute( $taxonomy );
	} else {
		$param_value = $product->get_attribute( $taxonomy );
	}

	/* @var WC_Product_Attribute $param */
	$yml .= '        <param name="' . wc_attribute_label( $taxonomy ) . '">' . $param_value . '</param>' . PHP_EOL;
endforeach;

Виноват. Вот верный кусок кода:

foreach ( $attributes as $param ) :
	if ( self::woo_latest_versions() ) {
		$taxonomy = wc_attribute_taxonomy_name_by_id( $param->get_id() );
	} else {
		$taxonomy = $param['name'];
	}

	if ( true === $param['variation'] ) {
		$param_value = $offer->get_attribute( $taxonomy );
	} else {
		$param_value = $product->get_attribute( $taxonomy );
	}

	/* @var WC_Product_Attribute $param */
	$yml .= '        <param name="' . wc_attribute_label( $taxonomy ) . '">' . $param_value . '</param>' . PHP_EOL;
endforeach;