Since I patched to Update 19 I get horrible game performance whenever I'm in combat. It seems to be worse the more creatures there are. My framerate starts to constantly stutter... and it doesn't seem to matter what my graphics settings are. I see the issue even when I have everything set to the lowest possible. I also see the issue in House Cannith and, to a lesser extent, in the Harbor.
I tried updating my video card drivers... didn't seem to fix the issue. I also force-closed all awesomium processes, and this didn't improve anything either.