First of all many thanks for this sample!
At Wonder Media, we are using DirectX 11 for our custom render and animation engine that uses glTF as model files, and we also made the open source Maya2glTF exporter. It's nice to see an open source glTF viewer based on DX11!
I briefly looked at the code and it seems your shaders are a bit older than the one in the Khronos PBR repos.
Specifically, my pull request that fixed shading non-uniformly scaled models is missing, and also this pull request that fixed a bug where NdotV can be >1.0.