Stencil rendering in MovieSquencer

When i use stencil render , the alpha of each stencil layer are not included ( pure black ), i have turn on the Alpha Channel Support to Linear color space only, and also set the frame buffer format, but still no luck with the alpha on the stencil when i put it inside Nuke, Althou, I can separate the layer using Shuffle nodes inside Nuke just Like Will did on his video, but when i switch my viewport to Alpha inside Nuke, it was all black. Any thought or idea on what i did wrong inside unreal?

Here is my setting inside Unreal:

I can seperate this using Shuffle nodes inside Nuke when Viewport RGB:

but no luck when i try to view the Alpha:

Any help will be much appriciated…