I've had some FPS mass fluctuation myself, quite a bit while running(dropping to 50-100); especially when i turned on my F5 window(dropping 1-5 from 290). I found out it was from double monitoring; turned it back to single monitor and the FPS stabilized. This wasn't the case with Nemesis 2 so hopefully there'll be a fix later.
gl on fixing that FPS; hf.