DC [servername] Online - Verify WinRM 3.0 service is installed, running, and required firewall ports are open

The Server Manager Dashboard is showing the error:
Verify WinRM 3.0 service is installed, running, and required firewall ports are open ....
I've tried various things to fix this and nothing seems to be working.

On the target:
The WinRM service is running and I've restarted it.
The firewall port for WinRM (domain) is open.
On the remote server:
I've run:
test-wsman -computername [servername]
and get:

test-wsman : <f:WSManFault xmlns:f="http://schemas.microsoft.com/wbem/wsman/1/wsmanfault" Code="2150859046"
Machine="DC1.contoso.com"><f:Message>WinRM cannot complete the operation. Verify that the specified computer name is valid,
that the computer is accessible over the network, and that a firewall exception for the WinRM service is enabled and allows access
from this computer. By default, the WinRM firewall exception for public profiles limits access to remote computers within the same
local subnet. </f:Message></f:WSManFault>
At line:1 char:1
+ test-wsman -computername DC3
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (DC3:String) [Test-WSMan], InvalidOperationException
    + FullyQualifiedErrorId : WsManError,Microsoft.WSMan.Management.TestWSManCommand

(If I run the same command and point it to DC2 the I get a reasonable result).

If I run this:

PS C:\Windows\system32> SC.EXE \\DC3 query WinRM

SERVICE_NAME: WinRM
        TYPE               : 30  WIN32  
        STATE              : 4  RUNNING
                                (STOPPABLE, NOT_PAUSABLE, ACCEPTS_SHUTDOWN)
        WIN32_EXIT_CODE    : 0  (0x0)
        SERVICE_EXIT_CODE  : 0  (0x0)
        CHECKPOINT         : 0x0
        WAIT_HINT          : 0x0

So, I've rather run out of ideas for how to tackle this issue.