I'd still be a bit careful when you see the message. The old school platform message was impaired sensor which you'd get in a rain storm / heavy spray. If charging down a motorway means you can't count on front assist to stop you hitting something. At that point ACC would be compromised.
The metal fence will be the radar bounce back is outside of parameters like heavy rain, spray etc and attempted calibration. I see two example above the white and the yellow referred too.