I have no idea, but it's a constant source of frustration. Sunglasses also lead to failed reads, which makes a little more sense but is just as frustrating. "Here's a new phone. It works great except you can't use it quickly if you're wearing sunglasses. Sorry!"
It works with some sunglasses. Probably related to the coating on the lens.
It works occasionally, but unpredictably. Consistently frustrating though
An ultra bright IR source from an unexpected angle?