My system specs can be found here: DxDiag.txt
Usually, the game runs between 40 and 60 FPS, but in some cases, which I am not sure what they are, the framerate will suddenly drop to 19 or even 9 FPS. The situation will last for a few tens of seconds, and then the framerate springs back to around 50.
I tried to lower the quality, but it didn't help, and I noticed that the problem still maintains even if I pause or quit a match. Also, there don't seem to be any premonitors before any sudden changes in the framerate.
So, I think there is a great probability that there is some optimization issue with the game. You might want to pay some attention to it.
(Yet it is possible that there is something wrong with my laptop.)