So, I liked this game so much that after completing it on GOG I went ahead and bought it on Steam too, just to support the devs. I figured I would write a very positive review (gave it 5 stars on GOG when it was still in early access), but since I had no achievements or gameplay time on Steam I decided to play it through again. Now, the game runs just as smoothly on Steam as it does on GOG Galaxy, but for some reason the dialog boxes and menus (including the main menu) respond very poorly. I have to double or triple-click to select a response or an option, which is extremely tiresome.
Please let me know what other data could help.