I just had this issue checking in. I kept uploading different .png and .jpeg files of my qr code, some the entire document, some just the QR code (I used the snipping tool), and it kept giving me an error. Finally I tried using the camera on my computer to scan a printout, that also did nothing at first, but after a couple of minutes waving the QR code around, it managed to scan it and allowed me to proceed. I'm assuming worst case you'd need to show your proof at the airport.