We are seeing an issue on Android/Unity similar to many discriptions as the "black screen" however it is on the second time the user accesses the AR.
1) User launches the app, goes to our main menu
2) User jumps into "AR Mode" plays with our sample
3) User exits AR mode back to our main menu
4) User returns to AR mode, and the camera doesn't appear to turn on.
If you kill the app, and restart (or reboot the device) the process starts over.
Unity 5.2.2f1 and Vuforia 5.0.5
Our app is on the Play store:
EDIT: appears to happen on iOS too, but on the third pass.
Our guess is a memory leak of some sort. Are we missing a method to shut down the AR cleanly? The app is broken into 3 scenes, main menu, AR, and puzzle scene.