Tesco Clubcard reward - corrupted QR code on email

Slinky

At the end of May I cashed out all my remaining clubcard vouchers for Prezzo vouchers, in 5 different batches. I've got 5 emails with the rewards, but on 2 of the emails the QR codes aren't showing. There's a tiny image in the box where the code should be. There's also a code next to each square, a jumble of random letters, does this represent the same thing? Do I need to contact Tesco or will the restaurant accept these letters as being valid?