Just noticed this spot in AU1. I put the start line there but the car drives like its on ice or something.

There are some spots like that. Also some spots where you can fall through the ground etc.
It is unfinished areas or just part of scenery and usually not reachable. only with tricks like autocross-editor

It's been there for ages, but if you want to drive on it, select AU1X (Press ctrl while selecting the track config) and place a start there. It should be driveable then.

Thanks Niko! That did the trick. Save me from trying to copy the lay where I could drive it.