Short Version:
Build 17639, both the LTSC and Semi-Annual versions, is missing the following DLL in the WinSxS folder:
Microsoft.Powershell.DesiredStateConfiguration.Service.resources.dll
It is normally located here:
C:\Windows\WinSxS\msil_microsoft.powershel..r.managed.resources_31bf3856ad364e35_10.0.14393.0_en-us_a944edf580471efa
Long Version:
I'm testing build 17639 of Windows Server to try out the new SQL Server support for the local pull server feature of DSC. I was trying to use the xDscWebService resource within the xPSDesiredStateConfiguration module (version 8.1.0.0), which is the "usual" way of installing a pull server, but I manually ran "Add-WindowsFeature Dsc-Service" before running the script with the xDscWebService configuration. Mostly, I did this just to check out the files, compare versions, etc. But once I ran the script, it failed with an error:
PowerShell DSC resource MSFT_xDSCWebService failed to execute Set-TargetResource functionality with error message: ERROR: C:\Windows\System32\WindowsPowerShell\v1.0\modules\PSDesiredStateConfiguration\PullServer\en\Microsoft.Powershell.DesiredStateConfiguration.Service.Resources.dll does not exist
This DLL is copied from WinSxS into the path in the error above when you install the Dsc-Service feature. I then compared this to a GA version of Server 2016 (non-Core but I don't think it matters), and that file does exist in WinSxS:
I did check the build 17639 system and that DLL is nowhere to be found in WinSxS, or anywhere else, on that server. I created the "en" directory as described in the error, copied the DLL over from the build 14393 server shown in the picture above into that "en" directory, and the resource was then able to create the pull server successfully. Additionally, it actually functions and writes to SQL Server as promised; bonus!
This post may be light on the info, sorry, but really it's just one bug report: that DLL is missing from WinSxS and is therefore not added during the installation of the Dsc-Service feature.
Edit: Sorry, had the wrong PowerShell window capture in there...