This is strange. I restarted my computer, and right now the game runs smooth. I didn't do anything right before the restart, but I've had my computer on for quite a long time, and during that time I uninstalled some codec pack (klcp or something) and some kodi player, along with nvidia gaming experience software. I had the gaming experience before (so I doubt that's the reason), but the reason I uninstalled kodi + some codec pack is because my game started running slower a little after I installed those stuff on my machine, as before them it was running smooth. It could be a coincidence, and maybe have more to do with something else.