I just confirmed this in-house on a 7970. Android device scans the QR code and finds it within seconds, iPad tried for almost 4 minutes before failing to find it at all. So the issue isn't the MFP, it is definately the app itself on iOS.
Try emailing the support team listed in the App store Print.Portal.Support@xerox.com
I see you already posted in the Mobile Print forum. and that is exactly where I would have expected you to get an answer since they are the support team for Mobile Print, and I would think due to that, the Print portal app.
The Xerox App Gallery is basically an app store on your printer that lets you download programs that will run on that printer.
Mobile Print is server software running on a computer and the Print portal connects to that.
The email DL is probably the best bet in this case.
The issue here is that you are trying to add a new printer via "Direct Printing" which is a feature that is not supported at this time on iOS v3.0.6. Current Android v3.1.01.88 from the Play Store supports direct printing which means it supports adding a local printer using the QR Code App. Currently a new version for iOS that supports direct printing is in development but we do not have an outlook for when this new version will be released. Keep an eye out for the next release! Thanks!
Is there a reason the option to use the QR code in the app exists on iOS in that case?