If the State and Country lists have been updated so the API values are set to ISO country codes the Masking of those fields during a data deployment does not work.
Data Load errors: '"FIELDINTEGRITYEXCEPTION:There's a problem with this country, even though it may appear correct. Please select a country/territory from the list of valid countries.: Billing Country:BillingCountry --"'

Disabling masking works around the issue.
It would be great if the application could check the State/Country list and utilize the API values for masking.