When you setup 2FA for some of your accounts, everytime you login into some platform, the message you get is "Identify Your Device", which send some numeric code to verify. But the truth is that, what QR code or Authority Keys do, is that they identify the code that was generated by the QR code identification, not the device. So, if you delete your account from your device, and setup the same device with the same account, your Authority 2FA will not work anymore, because it doesn't identify Your device, but that random code generated in the moment you can the QR code. This is not security, this is false security. Useful but false.