It's been a long time since I worked with QR codes. But when I tested a few years ago, there was a wide variety of quality in QR code readers, some were of questionable quality, Try downloading a couple other QR code readers on iOS.
I just tested this in InDesign and it is functioning perfectly on iOS.
In case you didn't already know you don't need to download an app on iOS to read a QR code. Just view the QR code with the camera (don't even need to take a photo) and it will automatically detect it and automatically prompt you as to whether it should follow the link etc...
As Steve already mentioned, the quality of different QR code readers is very hit and miss.