I’m pretty sure I know why it happens - if I try to set up the race with all cars in one bucket (by using year/power/region restrictions), I can get the race to start, but no AI driver will use a 328. In addition, I’m trying to start the race using an Alfa myself - if I use a 328, I can get the race to start. Both observations point to the game having an issue with the 328’s lower PI value - it will accept the Bugattii and the Alfa in one race because their PI’s are closer, but it refuses to let Drivatars choose the 328 because its PI is a tiny bit lower than that of the Bugatti…and if you set up the restrictions in a way that forces one bucket to use the 328, the game will get stuck on the loading screen becasue it can’t find a suitable car with sufficiently high PI value for that bucket.
Which in my opinion is a tremendously stupid restriction - I should be able to set up any combination of cars in freeplay, even if there’s a differnece in PI. The game even allows that without problems if you set up buckets with divisions - you can set up bucket 1 with Formula 1 cars and bucket 2 with Major Micros, and the game won’t complain. But if you use advanced options, it won’t let you choose cars that are more than a certain number of PI points apart. It won’t even warn you about that, it will just get stuck in an infinite loop when trying to load the cars.