The App Center Icon appears on the home screen.
The device is not visible in the App Center yet because the agent software has been dispatched but the rollout of the device has not been started yet.
Clicking on the App Center icon at the home screen results after some seconds (up to 20 sec) in to the error: Unable to Download Application.
Network connection is too slow and so communication has been timed out.
Not like TECH202938: Unable to Download Application" error when installing App Center client where an expired Distribution Certificate is cause of the issue. (The error message is a bit different)