I haven't used the QR promotion but have used similar promotions with Avis/Iberia regularly (~5x/year). I have never had a problem until December 2017. Since then I've had an Iberia promotion credit base miles plus the wrong number of bonus miles. I've also had an Avis/Emirates promotion only credit the base miles.

If the missing miles claim isn't working on the Avis website did you try claiming the missing miles through Qatar instead?