For the past few months I have had problems trying to run any of the Windows 10 UWP samples. Each attempt resulted in hundreds of errors. Yesterday, thanks to Colin Melia and a little Google spelunking I may have found the issue and the solution.
The Googling turned up https://github.com/Microsoft/Windows-universal-samples/issues/182 which indicates the same issues and that the problem may be with one of the references, Microsoft.NetCore.UniversalWindowsPlatform. Since I have been having issues, I did a clean install and installed the Windows 10 SDK. The issue appears to be that the samples were created with the 5.0 version of that file, but the clean install used 5.1. So when trying to open the samples, the reference could not resolve.
The solution was to open the project, in the Solution Explorer, right click reference and chose Manage NuGet Packages… Select Microsoft.NetCore.UniversalWindowsPlatform and select Update. I was able to do a Clean Project and Run.
No more errors!
Hopefully this will work for others.
Remember, if your solution contains more than one project, you probably will have to do this for each project.
Enjoy.
John Marshall… Visio MVP Visio.MVPs.org
john Visio MVP 
Thanks for the heads up John! Awesome info!!!! And great detective work! Thanks for sharing!