System refuses to let me update the monitor

I am trying to update the monitor registration information. As soon as I put in my MAC address and my email, it says:

Looking good: Device-Id and Associated Email are related…

I fill in all of the other required fields (even the ones I do not want to change) and I click “register”, and after a while it says:

Unknown device! Please check the “Device-Id (MAC)” and try again. NOTE: If you previously registered this sensor, you will need to use the same “Owner’s Email” as the first registration…

Why is it an “unknown device” when it was already “looking good”?