I'm on HW3, so FSD 12.x, but I've noticed this behavior as well. In my experience, it often (but not always) happens a fraction of a second before the light actually does turn green. I suspect the cause is that, instead of the neural network learning to treat the actual color of the light as the singular source of truth, it learned to also consider things that correlate with the color of the light, such as time since the light turned red, traffic in parallel lanes starting to move, and cross traffic stopping.