Update:

The pause/resume BTA issue should be fixed in the coming SDK 4.0 release (not the current "beta", but the final 4.0 commercial release that is expected soon).

This may be the same issue (there are some differences, but maybe you could check for the error message I posted to make sure): https://developer.vuforia.com/forum/issues-and-bugs/vuforia-fails-initialize-camera

We are also witnessing this issue. We have seen to occur with both the background texture access method and the regular camera background. If we background the application and immediatly reopen it the camera goes black. Timing is key, if you wait for too long before reopening the app then you will not be able to repro. 

Environment:

Unity 4.5.5f1
iPad Mini 2
iOS 8.1

There was definately a time duration component. The only difference between the Unity BTA sample app and what we repro'd on is using a different shader on the video feed plane, really. We were not using the native sample. Glad to hear this is repro-able on your end, thank you.

We tested the BTA (BackgroundTextureAccess) Unity sample app on the iPhone 5 (32-bit) with 8.0.2, and an iPad Air (64-bit) with 8.0.2, and an iPhone 6 (64-bit) with iOS 8.0.2. When putting the app into background on any of these devices and re-opening it immediately, we were able to get the app to hang on a white screen. If we counted off about 2-3 seconds before re-opening the app the camera was able to successfully re-init and work fine. When trying the native iOS BTA sample app, resuming it from the background immediately didn't reproduce the white screen. In your tests, are you using an unmodified version of the BTA Unity sample app? If you wait 3-5 seconds after placing app into background before resuming it, does it work?

Thanks shyamatdaqri,

it seems we could not reproduce it on iPhone 5,

but we did see the behaviour you reported by running the BTA  sample on iPhone 5S (both on iOS8).

We are investigating.

My response was in behalf of Wally.

We have experienced it on all devices which are on iOS8 and all versions of iOS8 (8.0, 8.0.1, 8.0.2).

Hi Wally,

could you also tell us what device you are seeing this issue on ? As dm3d said, we've not reproduced it here, but I wonder if the issue appears on iOS8 only on a few specific device models (?)

Also, the exact iOS 8 version (i.e. 8.0, 8.0.1 or 8.0.2... ) running on the device would be a helpful additional piece of info.

We tested the BackgroundTextureAccess sample app with Unity 4.5.4f1 and iOS 8.0.2 running on an iPhone 5 and were not able to reproduce the black screen effect when putting the app into the background and then restoring it.

iOS 8 introduced camera privacy settings, which if the settings for the app are turned off then the entire screen will be black, but that doesn't sound like the behavior you described. The iOS 8 camera settings is described in an FAQ here:

https://developer.vuforia.com/forum/ios/ios-8-xcode-6-and-vuforia-30-compatibility

For the crash happening when the app starts, this is experienced if you don't add the <key>UIInterfaceOrientation</key> and it's string value into the plist which is generated from Unity 4.5.4f1. This topic is covered in an FAQ here:

https://developer.vuforia.com/forum/unity-3-extension-technical-discussion/unity-454-and-vuforia-ios
 

Thank you for reporting this. We are investigating.