So my fire team of three was exiploring the Vault some days ago, glitched in through the door with intentions to explore. First off, if you haven't taken the first secret pathway you need to! Very unique, very peaceful. Its entrance is below the first chest.

Anyway, the point of this post was a 'glitch' we found off the side of the Templars arena. The far right conflux side has two hobgoblin platforms that can be traversed to reach a large rock shelf. From here, if you walk away from the arena, the lighting will change to a bright almost sunset glow, where it used to be gray fog. And if you walk back it switches back. The biggest visual treat is during the transition between light and dark you can see the walls of the cavern, its huge!!

Have not tested in normal vault, have not heard or seen this elsewhere.