This solution provides a workaround for a .NET Native (used when building a Master build for a Unity app built with the .NET backend) bug, where IInspectable pointers cannot be marshaled from native to managed code using Marshal.GetObjectForIUnknown.
To build for all Release flavors, run build.bat in the Visual Studio Developer Command Prompt for VS.
Otherwise, open the solution in Visual Studio and build with your desired settings.
Drop this into your Unity app in a Plugins folder, and the Windows Mixed Reality Utilities script will resolve properly.