Hmm, Unreal Engine (3 and 4) is basically one of the most annoying engines for SK to work with. I suggest opening SpecialK.ini - it’s located here if you’re using global injection: -\Documents\My Mods\SpecialK\Profiles\Batman Arkham City GOTY\
This is the section you’re looking for:
[SpecialK.HDR]
Look for this line and set it to True, and try the game again:
Promote8BitRTsTo16=true
If that doesn’t work, it might also help to enable 10 bit swapchain, but i’m not sure. A lot of tests to run but i’m not sure any will work, since it’s Unreal Engine.