AR Camera videoTexture vs video DOM

Forking the sample Hiro project that everybody uses, I have no difficulties using the AR project in its default mode – which is to have the videoTexture bool field in the AR camera (the camera object with the arCamera script attached to it).

If I fork the project and then replace the default FBX Playcanvas orange and blue “cubes” with another FBX 3D object that’s simple enough, again, no problems.

However, if I then replace these objects with a much more complicated (polygons and textures) that is also animated… I then have to set videoTexture to “true” if I want to have what the smartphone / web camera sees in the AR camera be reflected to the screen. Otherwise, nothing but blackness – EXCEPT the camera will still find and recognize the AR Marker … even though the screen is black.

Is there a simple explanation as to why this is so?

The project I am using to recreate this (sorry, it’s private; Can only share with Will etc) is here: