I'm not sure if I quite follow so please forgive me if I'm missing the point. There are two places in ARIS where QR codes can be scanned:
1) To skip the usual account creation step, making a random username and password (but still leading to profile creation as a first step) and (usually) logging into a particular game.
2) Within ARIS games, as a mechanic for connecting the real world and the one on the device.
Most of the time, I do not use 1. I have my own account and play games through that. But places like museums who don't need their players to have accounts and want to save the time use 1.
There is a potential problem in that since the account created is random, it would not be practicable to log back into that account, so if you do get logged out somehow, progress within a game is nearly impossible to recover.
It sounds like that may be what's happening to you. Maybe a crash is causing you to get logged out.
I do seem to remember some people reporting on a bug where profile creation where taking a picture would crash ARIS. Then relaunching the app would leave you back at the beginning, as you describe.
One thing that you might check on is that ARIS has permission to use the camera within ios.
One way around this might be to skip the QR code login and to use an account that was created on a device that was working correctly.
That bug may have been handled in the time since you posted too. I just created a new account and had no trouble.
Sorry for the delay, I've been unable to post for a while.