client ID manager startup.log can see below error

03-26-2021 18:53:41.885 ClientIDManagerStartup 7036 (0x1b7c) [RegTask] - Client is not registered. Sending registration request for 63e89b2f-1ebd-4f79-ab9d-d31d1c85529b7 ...

03-26-2021 18:53:45.682 ClientIDManagerStartup 7036 (0x1b7c) [RegTask] - Server rejected registration request: 3

At the same time if we look at MP_registration manager.log

03-26-2021 18:54:3.532 MP_RegistrationManager 27315(0x5AC4)

Rejecting the registration request because Agent Type is CD and registration hint is supplied.

SCCM setup to use HTTPS/PKI.

If we open the Control Panel Applet (Configuration Manager) I can see Client certificate: None

Here is the solution when we searched for the device in SCCM --> Devices and went to properties, it was showing its old unique Identifier but in Configuration Manager applet will show another unique identifier.

Delete the device from SCCM, then re-discover it from the AD system discovery agent.

Then clients will get registered and will show a unique Identifier on both the SCCM server and a client machine.