Hi there.
I have the following problem:
This only happens in iOS (iPad Pro, iPad Pro v2, iphone 7, etc...)
Unity 2018.1.4f1
Vuforia 7.1.35
Graphics API: (only) OpenGLES2
I deleted all UI elements in the scene, on Android, Windows and MacOS this doesn't happen. It also doesn't happen on other AR scenes in the same App. It only happens in two scenes. This one and way less "black flashes" in the other one. I can't find a commonality between the two scenes that the others don't share. Has anybody had similar problems?
Thank you for your time.
Since it's android issue only, I'm wondering if you are you using a depth mask material/shader anywhere in your scene? This is a common issue on some android devices. If so you'll need to edit the shader "Ztest always".
If not, I'd start by seeing if a blank scene or the Vuforia sample scenes exhibit the same behavior with your Unity/Vuforia install.