For such case, below are possible causes:
1. Running environment of the app
Recording with the face-cam is only activated when the app is distributed as ad-hoc.
Please note that it cannot be activated when the app is downloaded through AppStore after Apple’s examination.
2. Repro settings
Go to your app’s configuration page from "Settings" > "Tracking & Recording", and check if "User face recording" is turned on.
3. Device settings
The device with Repro installed will initially ask for a permission to use the face-cam with a pop-up dialog, something like:
Once you select "Don't allow," the device will not be able to record with the face-cam.
Please make sure the app has approved to record from "Settings" -> "Privacy" -> "Microphone" & "Camera."