Try to check the graphic settings on your Forza, because I've encountered this issue that even if you switch to 60FPS capped sometimes it get stuck to 30 FPS,
as far as I can remember you have option to select 30 FPS, 60 FPS, Non-Variable I think, regardless what you choose sometimes it get stuck with 60 or 30 FPS, try to select Non-Variable then close the program and run it again. it should, I was using GTX 1060 6gb and I was wondering why I am getting 30 FPS capped so that's the reason behind it.
There's one Gamer that was able to notice it as well I think it was shroud.