3D Linear Gradient not working as intended?

So I've decided to try out 3D Linear Gradient on a piece I'm working on. I watched tutorials and it looks very straight forward: Add fill layer, add black mask to fill layer, add generator and choose 3D Linear Gradient.

Except when I do that, nothing happens. Let me explain:
Basically, when I add a black mask to my fill layer, in the videos I would see a black square show up right next to the fill layer thumbnail. and when the 3D Linear Gradient is added onto the generator, you would visibly see the a gradient on the black mask thumbail. That's not happening with me. Here is a screenshot of what my layers look like:

I see a square with a black circle instead. I'm fairly new to masking and have only been using Substance Painter for a few months now. I haven't had to use masking for my projects until now, so I'm not sure what's going on here. 

Also this is what I've been seeing in tutorial videos:

As you can see, it does not look the same. Am I missing something here?

Thanks