We'll need some more information. What type of QR code is being used? CT-KIP or CTF?
If the code is a CT-KIP code, you should make sure the CT-KIP URL can be accessed by the mobile device. Typically a number of Web-Tiers are installed in a DMZ and share a public TLS name (i.e. what AM calls the "virtual host name") as a SAN.
If it is CTF, I would look for corruption in mail transfer for QR-code conversion.
Are there any logs at the server? Please enable verbose logging at the servers. Are you using Device Binding?
You may want to consider reaching out to customer support for assistance in getting your QR-codes working.
