I have noticed several times that the in game settings for the graphics has reset. Under Effects -> Particle density, I try to keep my Particle density at 200, since I have integrated graphics. It seems like maybe after the game gets an update, it automatically goes back up to maybe 2000.
Here are some settings that seem to change:
In Game -> Menu -> Settings -> Graphics
-> Map Detail
Shadow detail level
-> Effects
Particle density
-> Unit Visibility
Draw Distance