MicrosoftDavid Phillips we have experienced the same problem, I think I upgraded the MTR app to the latest version and it showed in TAC again.
Have a look here : https://docs.microsoft.com/en-us/microsoftteams/rooms/rooms-manage#remove-or-block-a-device
"When you remove a device, the device is removed from your organization and no longer appears in your list of Teams Rooms devices in the Teams admin center.
When you block a device, Teams no longer communicates with the device. Blocked devices won't be sent commands even if they're included in a group of devices that are being bulk-edited. It's still listed in your list of Teams Rooms devices with a status of Blocked.
Regardless of whether a device is blocked or removed, if it's still configured with a valid username and password, it will be automatically re-added to your Teams Rooms devices list if it connects to Microsoft 365."
