Weird 1x1 Crop When applying any kind of mask

What the heck is happening?

Trying to add a blur mask for some reason also crops the video file to a 1x1 square??

Here's what the footage looks like with the mask disabled.

And here's what it looks like enabled:

I tried to duplicate the clip so I could attempt a work-around using a opacity mask instead, but turns out the opacity mask creates the same annoying problem.

Any help would be greatly appreciated.