Just happened to randomly stumble across a reverse engineering talk about this very app a couple of hours ago:
The fix would be to allow the verifier to independently retrieve the license details after scanning the barcode, instead of just seeing a valid/invalid message.
Could a police officer just ask "I need to look up your license in the database. What is your name, date of birth and passcode so I can find your face in the database and confirm you gave me the correct passcode?"