The QR reader of the stock camera app works, always did. But it seems that a lot of apps use a different method to activate the QR reader or use a different library. Unfortunately it's not so easy to find out what they use because of closed source code.
Furthermore, QR codes on e.g. scooters are like 2x2 cm in size and with the S5 being further away doesn't work at all because all you get is a blurry white and black something. And there's no zoom function.