I bought the IMSA Track Pack over the weekend and haven't played since Sunday afternoon. I just popped in to play it today and the content wasn't there for me anymore. I've checked my purchase history and my DLC management screen (which says it's installed and activated) so I'm not sure what's going on. I tried a fresh install of the game with the same result.
Still not working for me either. Tracks were there in free period but after purchase not there. I verified integrity of files....100%