Woocommerce WC_Order -> populate(), unrecogonized characters in keys

I ran this code to read orders from a Woocommerce store:

Woocommerce - php to get order information

It works great, but this line returns an array with unrecogonized characters in it's key:

foreach ($customer_orders as $customer_order) {
 $order = new WC_Order();


provides an array with this key:


I would like to access this key in my code, but I can't read what those unrecognized characters are.

I ran it through UTF-8 htmlentities, but no luck.

I have workarounds, but it's easier if I can write out that key.