Am also facing the same issue. camera is off and showing black screen.

This is not every time. it is happening 20-30% of chance.

I have created a new post. please refer for total details : https://developer.vuforia.com/forum/device-support/black-screen-ios-devices-camera-mode

Any quick fix solution would be appreciated we are quite in a hurry!!!

Thank you.

Hi David,

Thanks for the response. This occurence does not seem to be consistent, and by my estimation there is a 10-20% chance it will occur each time the application is started.

Another note: The onDrawFrame() callback is still firing periodically like it would if the application were working.

Is this occuring consistently, if not what's the frequency?

I experience this same issue with the Nexus 10 hardware on Android 4.4.2, Vuforia 2.8.8 while running both the Native and Java sample applications. 

Note: The failure pattern is as follows:

"E/BufferQueue﹕ [unnamed-1637-1] dequeueBuffer: BufferQueue has been abandoned!" is generated when closing a working instance of the application.

The application is restarted.

During startup, "W/CameraBase﹕ An error occurred while connecting to camera: 0" is repeated nine times in the Logcat.

The call CameraDevice.getInstance().init(CameraDevice.CAMERA.CAMERA_DEFAULT); returns false.

The device must be restarted for the camera to function again.

Not to hyjack the thread,

But I am aslo getting this problem often. Using sony tablet s with vuforia 2.8.8

As you said, the restart fixed the issue;

have you been able to reproduce more black screen occurences after the restart ?