@yoss Sorry for the very late reply. Kind of missed this one. I just took a screenshot that highlights the issue. If you compare the Ferrari with the Porsche, the shadow under the car seems to be missing completely wich makes the car look like it is floating. In the showroom it seems to look ok, but on track it's missing. Maybe the undertray shadow is placed too low or something like that. I am not exactly sure how it works but aren't you placing a plane under the car? Maybe that needs to be raised a littlebit. Here is the screenshot:
View attachment 49996
As you can see the shadow under the Porsche in the background, I don't think that this is a LOD issue. But might be worth to check this aswell to rule out all possible causes for the problem.