So about 6-8 seconds or so, as the car was still accelerating most likely. There is also probably a slight delay for AI based driving after speed limits change, so probably closer to 4-5 seconds later.

That actually sounds like a potential corner case - braking while still accelerating. I'd hope to all that's holy that sort of corner case comes up in your first million miles of testing and not basically in production, but it sets my debugging nose a-twitching.