I'm also having this issue, especially in Revenant's Toll. Pre-patch I was easily getting an average of ~45 FPS on ultra, now I'm down to about 5 in crowded areas, the game is literally unplayable at this point. Lowering the settings seems to have no effect at all. I've tried the obvious things like restarting my PC, closing all programs running in the background, even Windows explorer. It's not my network, every other game I play runs just fine. Restarting the game temporarily alleviates the issue, but it's back to laggy in a few minutes. I'm baffled.