Rendering with a mask? Why won't this work?

Hey guys. I just started using hitfilm express 12 and I have what I feel like should be a super simple thing, and it isn't working. I can't figure it out.

I have a composite shot with two png images. One of them has a mask in the shape of the other. It's working beautifully when I scrub through my timeline and preview it in the editor. The problem is that when I render the video, only one of the png's is there. The one that gets revealed never shows up. What the heck.

In one screenshot you can see the text is halfway revealed in hitfilm, and then the second screenshot is the rendered video.. no text..