ARFoundation 4.0 iOS - AR uses wrong camera, ignores camera facing setting

Hello,

I recently updated all my AR packages to the 4.0 preview. Since then, I've followed the example in the ARFoundation samples to add light estimation to my AR app. As the sample stated that light estimation only worked when face tracking was on in iOS, I also added a face tracking manager to the AR session.

Everything is working fine on Android, but I've hit a huge problem in iOS. Although my AR Camera facing setting is set to the world, the app is using the front-facing camera. I thought this might be because the face tracking manager was overriding it, so I removed that manager from the app. However, the app is still ignoring the camera setting and using the front-facing camera and I can't get it to show the back one.

How is Unity deciding which camera feed to use? Is there an implicit override somewhere that I'm not aware of?