Script AI Manager acting strange on different surfaces?

For a while now, I've tried to get AI working on many different dirt roads in the game, but the AI acts weird and drives slow. I have linked a video that shows both a Sunburst and the new Dunekicker driving on dirt using the AI.

You can clearly see the AI driving slow and not working properly when on this dirt surface. In the video is also the Sunburst driving perfectly fine on the West Coast race track and it is not because of the specific map.



If anyone knows what causes this or how it can be fixed it would be much appreciated.

 

I am also having that same issue. On mud, the cars drive very slow :\