The other day, the pulsing blue color on the display was instead red when asking me to apply torque to the wheel. Also, the normal sounds of turning on and off autopilot were different. Echoey and doubled. It corrected itself after a mile or two.
That just means it wasn't a nag, but rather a more urgent "I don't like what I see, I may need you to actually take control in a moment". I've seen this when lane markings are super faded (or non-existent, or screwed up because of construction).