Make sure you’re using Merge Cube in a well-lit area. If you need more light, the app has a feature that will turn on your device’s flashlight. Tap the menu icon, then tap the flashlight icon.
If you lose the augmented reality layer and see the physical cube, you might be holding your Merge Cube too close or moving it too fast. Your hand might also be blocking the cube’s graphics. Try slowly moving the cube so that a flat side of the cube is facing toward the camera, or try repositioning your hand.