So they had an issue with the car slamming on the brakes at unexpected times, caused by misidentifying cracks in the road or glare or weird lighting or w/e. The solution was to make the cameras ignore anything they can't recognize at high speeds. This resulted in Teslas plowing into the back of firetrucks.
As the article mentioned, other self-driving cars solved that with lidar, which elon himself is against because he says AI will just get so good and 2d cameras are cheaper.