It doesn't take much for our tiny flanges to skip over a small irregularity. With 6 wheel trucks on diesels, they pivot about on the center ones if there's the slightest high spot. There was a turnout on the club layout that was old, the tip of one of the point rails had dropped just a tad on the diverging route's outer track and wheels would just ride over it onto the wrong track. Once one went the rest would follow.