One of the new features that came out in SCCM Current Branch 1806 was the ability for the SCCM console to show the currently logged on user.

I had an issue where this field was blank. First thing I checked was that the SCCM client on the device was up to date (1806 or later)

On all clients, in the ccmmessaging.log I noticed:

No reply message from Server. Server may be temporarily down or a transient network error.
Post to http://<mp>/ccm_system_windowsauth/request failed with 0x8000000a.

Then when checking the IIS status codes on the Management Point IIS logs it said:

CCM_POST /ccm_system_windowsauth/request 401.2 (401.2 – Logon failed due to server configuration.)
CCM_POST /ccm_system_windowsauth/request 500.0 (500.0 – Module or ISAPI error occurred.)

This was due to Active Directory User Discovery being disabled in my site.

Once it was enabled and the users were discovered, the errors went away in the ccmmessaging.log and as well as the MP IIS logs. Now the Last logged on username appears in the ConfigMgr console.