The problem
Although they all appear in the account, when a customer looks on the "My Products" not all the devices are listed.
This happens if the devices have been deleted for some reason - either deliberately or perhaps when a location is removed from the app (e.g. when changing from a physical hub to a virtual hub).
If you then try to add the device back into myaccount a warning message to say the device already exists. That's because the device still exists in the database but it's been marked as deleted.
The solution
The answer is to add the device as if it not connected to the internet.
In myaccount dashboard select the "Manage Products" tab.
At the bottom of this screen select:
Then, at the bottom of this screen select the option to register a product that is not connected to the internet
The select the correct product icon and enter the device serial number
Click on "Next" and your device should appear in your list of products