Solved

race started without one car

Was it the new driver who went missing the race? You probably sold the predecessor without making the new one active in the drivers & staff tab, by doing that the new driver appears to take the vacated seat automatically but often that doesn't work properly. Although if that's the case then usually the new driver refuses to do training laps as well and instead complains about repairing the, in perfect condition, car. Did you let her do training laps?

If that's the problem then to fix it go to the Drivers & Staff tab, Click the green Change button, select your drivers again and click Confirm. Else Yunus or José will have to take a look at your team.