Hey, could you upload a screenshot with "Edit" tool enabled, so it would show the Bezier curve control points? One of those points will likely be dragged very far away. While in the Edit tool, try to drag it back closer to the rest. Try to look further around the edges, it could be that this point is so far that it's not easy to notice.

If you see nothing wrong around the red cross, it could be that there's another issue there that doesn't get displayed while the control points being too far away is resolved, so don't focus too much on that single point.

Thanks for the answer, as I can't save the track, I just quit. Whichever point I moved, alleged error I fixed, there was always another one somewhere else.

My guess is I've gone over some Unity limit and things get sideways internally, tracks was a pain to load and drive in testing (have you seen it was over 25 kms ?) Already experienced poor unity objects model with Kerbal Space Program, when there is too much, it just doesn't work. That's may explain all tracks are so pretty short. Did you tried 10 kms or more closed/opened tracks ?

I could eventually try to make another long track but I don't think it would be useful. I generate an open track then add more and more points after the end, run around, goes back to stay on the map limits, then generate items.