Windows Server 2012 R2 upgrade to Windows Server 2019 fails

A customer is trying to upgrade Windows Server 2012 R2 to 2019. The initial phase (including updates) gets to the point where it states that the system will restart in a few moments. However, shortly after that (but before the system restarts), the message is displayed that the installation failed.

The C:\$WINDOWS.~BT\Sources\Panther\setuperr.log appears to indicate that the error that caused the failure was:

Error [0x080389] MIG Failure while calling IDiscovery->Gather for Plugin={ServerPath="Microsoft-Windows-AppX-Deployment-Server\AppxUpgradeMigrationPlugin.dll", CLSID={AE27C1A6-25F2-45FD-9A28-081B81F29E0A}, ThreadingModel=Apartment}. Error: 0x80073CFE

Error MIG Error 0x00003CFE while executing critical action Action,CMXEPlugin,C:\$WINDOWS.~BT\Sources\ReplacementManifests,Microsoft-Windows-AppX-Deployment-Server\AppxUpgradeMigrationPlugin.dll,{AE27C1A6-25F2-45FD-9A28-081B81F29E0A},Apartment. Migration will abort[gle=0x000000cb]

Error Gather failed. Last error: 0x00000000

Error SP . . . (omitted these lines)

Error SP ExecuteOperations: Failed execution phase Finalize. Error: 0x8007042B

We ran Chkdsk and SFC /ScanNow, but neither found any issues.

We then tried DISM /Online /Cleanup-Image /CheckHealth, which reported:

The component store is repairable.
The operation completed successfully.

Next, we tried DISM /Online /Cleanup-Image /RestoreHealth, but that failed reporting:

Error: 0x800f0906
The source files could not be downloaded.

Research indicated that the download issue might be caused by a Windows Update issue. So, we tried a few of the many published methods for resetting Windows Update services (including the PowerShell script provided by MIT: https://gallery.technet.microsoft.com/scriptcenter/Reset-WindowsUpdateps1-e0c5eb78). None of them worked to allow DISM to download the source files.

Can you offer assistance to get DISM /Online to run (or fix any of the other errors)? Thank you!