Quote from Zantai:
That said, for anyone having issues launching the game after the latest V1.0.2.0 update or have experienced problems with visuals or loss of FPS, please try the following:
- Verify Game Files in Steam
- Run Repair.exe located in your Grim Dawn install folder.
- Delete Options.txt from \Documents\my games\Grim Dawn\Settings
If none of those work, add “/d3d9” to your launch options for the game.
How to set Launch Options:
https://support.steampowered.com/kb_article.php?ref=1040-JWMT-2947
The /d3d9 part will most likely solve your problem.