Restart the Shell by removing and reinserting the card, or pressing on/off button. If issues persist, remove the battery and reinserts it.
Keycard Shell: Check that a Keycard is fully inserted in Keycard Shell. if the problem persists, check the BL-4C battery charge. Replace or recharge if needed.
make sure the full QR code fits in your screen while scanning and try no to move too much.
Tip: you can get some good results by moving a bit further sometimes.