First I was working on a window that cuts through the first floor and the second floor which is seen at the third image I attached. I used a cutout for the floor that is in the middle but it is also at the same level of the cutout for the hole in the staircase, I deleted this cutout as shown in the second image but I noticed that the floor hasn't shown itself then I looked further and saw that the whole floor of the second floor is gone. How to fix this?