So after googling, searching the forums and playing about with the Camera API I have found absolutely no solution and could do with a helping hand on resolving this issue.
The issue that I faced, that many on this forum seem to have faced, is the AR Camera rendering dark when using the front/back camera. The AR camera was rendering perfectly on any Android version below 6.0, until some of our users upgraded their devices (mainly Samsung) to 6.0 and 7.0 (Nexus 6P) and this is where the dark camera appears. To me it seems as though the auto-focus just isn't working and therefore not adjusting correctly to the lighting conditions.
I have provided a video link on the next line comparing our app running on Android 5.0 (device on the left hand side of the video) and Android 6.0 (device on the right hand side of the video):
I've already tried these attempts at a solution to no avail:
1) Changing the target sdk version to 22 from 23
2) Looking into the Camera API and adjusting different settings such as the exposure lighting and ISO values
3) Downgrading the Android version from 6.0 to 5.0 (as stated above this worked successfully but when upgrading to 6.0 the dark camera appeared again)
If you have any ideas on how to resolve this issue I'd be extremely grateful. I'm currently using Unity as the development package and building to Android.
P.s The error also appears when you download the latest Vuforia sample from the website into Unity and then porting over onto onto an Android device. The AR camera uses 'CAMERA_FRONT' as the 'Camera Direction'.