Did you generate the QR code with the most recent version of the user app?
If you scanned a QR code that was generated by an older version of the user app, that might be the problem. If this is the case, delete the CSV file on the master app device, which is located on the SD cards root directory. The file should be called something like “match data”.
Then update the user app.
If this is not the case please let us know.