Thanks for playing! ❤️ We weren't actually aware of the crash bug. Do you mean it happens when you finish one playthrough, then start another one? Anyway, that's the first thing I'll investigate when I have time :)
It does indeed seem that my design of the fog of war was far from perfect - a tile of perfectly flat terrain looks identical to an undiscovered tile, which can lead to confusion (especially when an undiscovered tile is between two discovered ones). Something to improve in the future.