Failed to mount Elastic Layers, "A virtual disk support provider for the specified file was not found."

When using Elastic or User Layers, they do not get attached to the end-user VM when the user logs in. Checking C:\ProgramData\Unidesk\Logs\Ulayersvc.log, you see an error like this: 2018-07-19 13:02:25,804 ERROR 16 CompositingManager: Caught exception:...