I just ran into the same issue as well. For me, the area was running smoothly until I entered the torchlit underground cave area (where there's the warrior-smash-able walls). Now it's unplayably laggy and nothing seems to alter that.
Interestingly enough menus, dialog boxes (such as the 'requisition' system), etc., continue to run fine in that area. It just takes a second or more to render each frame when the main game screen is active. Disappointing as I was super excited to explore Solasan! ☹️
