Unreal Engine 4 is available for Win10 UWP app dev now

When I run WACK on my shipping package, I get the following error -



API D3D12SerializeVersionedRootSignature in d3d12.dll is not supported for this application type. MyGame-UWP64-Shipping.exe calls this API.


I can’t see a direct call to this function anywhere in the source, and I’ve even got DX12 disabled in Win10 UWP builds (via the bUseD3D12RGI flag in UWPTargetSettings). Any thoughts on where this is coming from and how I can remove it?