Are you clearing Z-Buffer to 1.0f?

Can you see the error?
 

D3D12_SHADER_BYTECODE vertShaderBytecode = {};
vertShaderBytecode.pShaderBytecode = reinterpret_cast<UINT8*>(mvsByteCode->GetBufferPointer());
vertShaderBytecode.BytecodeLength = mvsByteCode->GetBufferSize();
psoDesc.VS = vertShaderBytecode;

D3D12_SHADER_BYTECODE pixelShaderBytecode = {};
vertShaderBytecode.pShaderBytecode = reinterpret_cast<UINT8*>(mpsByteCode->GetBufferPointer());
vertShaderBytecode.BytecodeLength = mpsByteCode->GetBufferSize();
psoDesc.PS = pixelShaderBytecode;

I installed RenderDoc but I was unable to make use of it, because I am having the Dx12 code inside a DLL invoked through COM by another program and the UI was not so intuitive for me. So I had to add tons of code to print back the content of resources(shown in the picture). Once discarded the buffers as the origin of the problem, I used the helpers inside D3d12.h(what I do normally is avoid D3d12.h at all because I want to learn better how Dx12 works). I noticed that changing my code for CD3DX12_SHADER_BYTECODE is making it work and that made me localize the error that(I'm sorry for this) has nothing to do with Dx12.

Well! That triangle was tough!

It is a stupid copy paste mistake, you put the pixel shader bytecode and size to the vertex variable on , and ends up with an empty pixel shader struct. That is all.

You would have found that in 2 min with a capture in PIX, as you would have spot the missing pixel shader stage !