hwp_product_gtin Not Available Product Feed Pro

I had a client install WooCommerce UPC, EAN, and ISBN By Scott Bolinger so we could add GTIN to the product feed. The client started adding in GTINs for various products without issue, but when we went to add the field to our feed, we discovered that the GTIN field (hwp_product_gtin) is not showing in the dropdown selection when we try to modify the field mappings. Any idea what could be causing this issue? I’ve already tried deactivating/activating both plugins to no avail.