Hi crincrin
I am aware that with my window 7 I am a dinosaure😁 . It will change when my bank account will permit me to change my PC (hopefully in a few months).
To answer your questions :
The Mega window does not have a problem in my game.
I have never changed the GraphicsRules.sgr file.
As for my graphic settings they are all at maximum. Lowering them does not change anything.
I did not look in all the worlds, but I have seen it in Henford-on -Bagley, Tartosa and Britechester. But as I said it is selective. I think I will try reinstalling the game.