I´m getting the same error message – also using WooCommerce-Germanized and woocommerce-jetpack.
I´d be great if your developers could fix the problem timely.
Thank you so much for your support.
BTW: We are currently running a test to see if the following change in line 81 of the class-wcj-product-by-user.php will fix the problem:
The original line 81 reads: $useremail = $this->getProductOwnerEmail( $order->id );
The proposed solution of our developer is the following:
$useremail = $this->getProductOwnerEmail( $order->get_id() );
I´ll report back if this solves the problem.
Greets
Mirko
