You will see a small hotfix hitting Steam very soon. It contains the following changes:

  • Additional changes have been made to further improve framerate for players that saw a decrease in FPS after last week’s game update.
  • Based on player feedback the ability to toggle shadows on/off has been added to the in-game options menu. However, as with other gameplay rules, we may enforce shadows to be turned on for some game modes or events in the future.

Source: Reddit