Are you shutting down all non-essential programs (especially anti-virus) before starting the game? Firewalls have also caused conflicts.
For the Steam version, did you try verifying local files? In the Steam library, right click on Divinity Original Sin and select Properties, switch to the Local Files tab and then click on the 'Verify Integrity of Game Cache...' button.
For the GOG version, you could try re-installing.
