DetectFaceRectanglesRequest most likely is not supported on CPU and will therefore not run in the simulator. You need to run on the physical device. Similar post here.

@cheesenuggit What is your plan? I'm not sure how to approach this.

+1 Wondering if the Swift Student Challenge judges will be able to use it. Do they run the projects on a physical device or in the simulator?

Alright, after around 30 minutes of searching, I found that I could just use Apple's "Reality Converter" to make the USDZ work. I had a character rigged to an armature with a simple animation. The USDZ exported from "Reality Converter" worked in "Reality Composer".