Undefined Variable errors

Hi, This plugin is great but i have ran into a few issues.

If i save the tracking information but do not mark as shipped and manually change the status to shipped and click update, i get 2 errors within the email sent to the customer stating that there are undefined variables on the following line: “1624” located at woo-advanced-shipment-tracking/includes/class-wc-advanced-shipment-tracking.php

Any ideas what might be causing the issue?

Cheers