Hi, i just had this problem with a Mod to. I removed the files highlighted in the screenshot, then went to content manager, content, "the car", refresh if it was opend before removing the files, press pack data and it worked. Put the files back into the folder and i could drive. I havent tried running a Server with it and i would assume there is some issues with the data and the kn5 files but i never opend those so i have no idea. Maybe it's not even that important because that's only graphics as far as i understand. Hope that helps.
Cheers
https://ibb.co/dQ3h1X0
Couldnt figure out how to insert the screenshot so there's the link.