If you are working in the editor when you start up Vuforia AR a game object gets created call "New Game Object" (good choice of name....) Attached to that gets created an Emulator Ground plane object. If you then either disable the AR camera or the Vuforia behaviour script on it that emulation game object is destroyed. Re-enabling the AR camera or the script doesn't bring it back so it becomes impossible to test in the editor. How do you get that object back? or are we meant to just make one of our own?!? Vuforia really is the worst framework I have ever seen in Unity, I hope that the Unity devs bring this in house at some point, it really is letting them down to have included it in the state it's in.