I've had a bit of difficulty with the AI for a long time now. I've had aggression set at medium. The AI will make late dives into corners. Will make late blocking moves. They will brake check you in the middle of slower corners. Push you over off the track on a straight. If you've out braked them coming into a corner they are likely to just run into you. Just all kinds of nonsense.
Last night it was a big problem. I was trying to run a F1 V10 Gen 2 race at Barcelona 1991. AI strength set at 90, 10 laps, medium aggression, starting in 10th. After 16 restarts and it was nearly midnight, I just gave up trying to finish that race. 2 of those were my fault. I ran too long into turn 1 once and went off track and once I locked up going into turn 5 and slid straight off.
But outside of those two times it was clashes with the AI that ended all of those races. They would run into me after I out braked them into turn 1, they would brake check between 7 & 8 causing a collision, slow down at turn 12 causing a collision, etc.
So today when I went back to the game I thought I would put aggression on low and see what that did. I didn't run that F1 V10 at first so I tried it in some other classes. I ran a Maserati Trofeo race, a GT3 race, and a 90's F1 race. The AI felt much better. Wasn't making those late diving and blocking moves. Didn't crash into me while I was trying to pass. So I went back and ran that same F1 V10 Gen 2 race at 1991 Barcelona. Finished it in one attempt that time. Racing was much cleaner and seemed more fair. So I'm going to leave it on low for the time being to see if it stays good and that wasn't just a one day thing.