Certain locations in maps either become white/light blue or transparent when viewed from a distance. In the latter case (transparency), huge chunks of the world appear to be removed, letting you see through to distance subterranean areas. If you close to within a few dozen blocks, the transparency glitch disappears.

But it happens reliably in the same locations in the same seeds. (I can share seeds, but can't share coordinates, since not implemented yet.)

(Also affects MCPE 1.0 on iOS 10.2; I tested using the same seed, same location, had the same results in same locations.)