Why doesn't Directory.Build.props work when building a solution using Visual Studio 2017?

I had added the directory.build.props as a solution item. This somehow prevented Visual Studio from picking it up and using it in the build process. Once I removed it as a solution item, this worked fine.

You also might have to delete your .vs directory (or portion of) as it seems to be cached there as well.

https://developercommunity.visualstudio.com/content/problem/248037/defaultbuildprops-with-langversion-is-not-used-by.html