I've noticed this issue appearing occasionally on some android devices (Pixel and Galaxy S8).
Sending the application to the background, waiting several minutes and then restoring the application. Causes the camera to show a single frame and then stop updating. I have attempted to restart the camera (CameraDevice.Instance.Stop, CameraDevice.Instance.Start) upon restoration along with restarting Vuforia by toggling the behaviour on and off. This appears to have no effect.
As far as I can see the application is still receiving frames from the camera but it is just not updating the background for some unknown reason.
Has anyone seen this issue before? Am I missing something for debugging?