Game switches between 60 and 30 fps

[Jim]

Penumbra: Overture was the same. When I was recording, my FPS was very low. Maybe OpenGL system cause this. Or your system isn't strong enough. What happens when you recording other games?

It's not that I'm struggling to get good fps, it's that the game intermittently locks me at 30 and I don't know why. I should have mentioned that I have a nice rig and performance "shouldn't" be an issue:

i7-4770k
Asus Sabertooth Z87 motherboard
PNY GTX 560ti
2x8GB Corsair Vengeance RAM

Edit: And to answer your other question, yes, I have seen this before somewhere. I can't for the life of me remember where though. I know I never found a fix for it.