I literally was just looking into this the other night. I reduced the number of AI but I don't know if I was working with less than 21 AI.
Anyway, when I would start the race session with a rolling start, I along with all the AI would start out in space below the track, free fall for a second then plop in the garage spaces and the AI wouldn't do anything. Looking into the AIW I noticed the alt grid positions were set out in space below the track. In the AIW I simply copied all the "grid" spaces using a text editor and pasted them over the alt grid positions. When I rolled over to a race session it worked everyone lined up on the front straight and rolled off with the pace car.
I was going to see if I could contact the original author to update the track with my re-packaged track. I can try to upload it and provide a link to my version for you this weekend.