I am using Unity with Vuforia for an AR game, and I have an infuriating graphical glitch (which only appears on device).
It appears to be the same issue described in this post; however, unlike his last post says, all my testing only confirms that this is a Vuforia issue and not a Unity one. (Unfortunately, he did not go into the process that led him to believe otherwise, so I can't compare our results. Even more unfortunately he did not describe how, or if, he ever fixed the issue.)
Because when I created a reproducible test case from scratch, I don't see the bug until I add in Vuforia. In fact, if I put the Vuforia object and the render-texture objects on different scenes, I don't see the issue until both Vuforia and a render texture object exist! It's absolutely clear that Vuforia, itself, is mucking around with render textures that should be outside of its purvue. How or why, I don't know, but it's definitely happening.
Here's the setup:
Scene A: Loaded on startup. Contains the UI and nothing else. A Canvas, a RawImage linking to a RenderTexture asset, and 2 buttons - one that additively loads Scene B, and one that spawns Prefab C.
Scene B: The most basic possible Vuforia scene. An ARCamera, a Cylinder Target (any target will do), and a cube attached to this target so it has something virtual to show.
Prefab C: Contains a camera which renders to the RenderTexture assets that is displayed in the UI, and a few objects to render (cubes and a character, in my case.) Contains a second camera in identical position/etc, but instead of rendering to a texture, it renders directly to a corner of the screen. The second camera confirms that it's Render Textures being messed with and not, for example, a Projector or light source affecting the objects being rendered.
In the editor, all these these function as expected. When I click Spawn, the character/cubes appear in both the direct render and the render texture. When I click Load, the AR scene is loaded and my computer's webcam is displayed. Regardless which order I click these things, they do not interfere or interact with each other in any way. And my render texture looks normal.
Then I build to the device. When I click Load, the rear camera is activated and the AR scene is loaded. However, when I click spawn, the rear camera is no longer visible in the main view. The direct-rendered Prefab C is rendered properly in the corner, but the render texture is invisible. However, when I click Load a second time (which is now injecting a second AR camera into the scene, BTW), the rear camera is still not visible, but the prefab IS visible - exhibiting the weird bug where the physical camera's captured iamge appears to be double-exposed overtop of the render texture. To me, this is the smoking gun that unavoidably implicates Vuforia as the culprit in this bug. Loading that scene SHOULD NOT have any effect whatsoever on any part of that chain: the objects being rendered, the camera, the render texture, the UI all exist entirely outside of what should be the realm of Vuforia's influence. And yet, here they are, being altered by Vuforia (and also interfering with Vuforia's functionality, as well).
My hunch is that Vuforia, when it launches, is for whatever reason groping around the scene to find any RenderTextures it can get its hands on, and assuming that those RenderTextures MUST be the ones it needs for its own functionality, and just claims them for itself. That's what appears to be happening based on this test.
If anyone has a reproducible case where using a Render Texture does NOT get messed with by Vuforia, I'd like to see it. I haven't seen one work yet.