Prestige mode not working, Achievements not unlocked.

Hey can you explain how the Eddie challenges work because one time attack I'll be smoking them beating my time for the 1st 3 laps, but if I smoked them how are they able beat my lap time 1 min before the race is over if they can't even catch up to me? The challanges don't really explain how the grading system functions. Do I get a time penalty for hitting a sign or something? I just wanna know so I can adapt and progress. Same with the prestige times, the second of spikes races doesn't even show the times I need to beat in order to get better than bronze. Also why do I need to have to buy the fastest cars to beat the prestige races, if I can smoke a super up lambo in regular story on hard when I have maxed parts then why shouldn't I be able to keep up with them in prestige mode? Do they (A.) Have higher grade parts that I can't buy to make it difficult or (B.) Did the developers modify the cars driving stats so that even slower cars that shouldn't drive that fast keep up with cars that would beat them? But if that's the reason, fine I'll by op cars and max them for specific races, but I would like to at least have the garage slots extended so I can keep my original cars I actually like, plus the boss cars I earned. Because if I have to sell my personal self expression cars because I have to have an exotic or specific car to beat an event than in my opinion it's not the car it's the event