I had problem with SC2018 mod. When I try to make skin pack for league use game UI always get Team names as Class names and put team to different class as it multiclass racing. With Dallara IR-18 I was able to override this behaviour by adding DisplayClassOverride="IC22" string in Upgrades file. But same trick does not work with Stockcars. Attached couple of my veh files and upgrades file to this post. Steps to reproduce. Download carset from workshop. https://steamcommunity.com/sharedfiles/filedetails/?id=2916035920 Start single player with 20AI with that mod. After track loading you will see UI in multiclass mode with team names as a class name.
I don't think the team name should be included in the Category parameter. Maybe that was done to separate the teams on the car selection menu, but it might have this unintended effect.
That is explain why default SC2018 had such a strange categories order. We use scheme with teams as a category for many years and only Stockcars give us problems.
Ok. Now I deleted all subcategories and all work as intended. Game somehow uses Category tag as Classes. I don't know why.