Notes:
1. I encountered this issue on PC
2. I was playing ALONE
3. I was playing as Drizzt
4. I could avoid this by rotating the camera to avoid looking at the graphics in question

Steps:
1. Load The Order of the One Light - Return of the Tyrant mission
2. Get to the last boss
3. Fight boss until "green" phase where poison/green attacks are used

Result:
I experience very low FPS when viewing the unblockable long-lasting "green cloud" attack (cloudkill?) which follows the player around. The rest of the fight has a higher, consistent frame rate. When this one attack is used, my framerate appears to drop to the point that I cannot effectively play the game.

Expected Result:
Frame rate doesn't seem to drop and I am able to play at an expected fps.