Hi,
The only reason I can see these warnings would appear would be if all the custom address fields would be disabled.
So that's quite uncommon, and that might explain why we didn't get the issue and no one else reported it so far.
Removing the warnings can be done by adding the line:
if(empty($this->order->$fields_type)) return;
after the line:
$fields_type = $this->type.'_fields';
in the file administrator/components/com_hikashop/views/order/tmpl/show_address.php
We'll make a more complex and cleaner patch on our end for the next version of HikaShop.