Please give the following instructions a try:
1. Open up the tuning interface for a official S397 skin of the Porsche.
2. Use the buttons at the bottom right to first create a dir(ectory) and to then reload the skin.
3. Afterwards you should be able use the < > buttons to switch to ALT.
4. Now create a alt-skin by using the create button and type in random stuff like "test" "test" "test" "0".
5. Please quit the game now and check out the skins folder in UserData/player/Settings/Porsche_911_GT3_R_2018. You should find .rcd-file named by a single number like 3.rcd.
6. Open it up, copy VehFile = *.VEH line and replace the one in the Robichon.rcd-file with it.
You should be fine now.
If it solved your problem, please let me know the new .veh-file name so I can change it for everybody who downloads this skin.
All the unnecessary folders and .rcd-files can be deleted afterwards.
