Ok, I downloaded the lot this morning and spent the last couple of hours trying to find a way to get the stair base to show up on those stairs. Sadly, without much success. I get what you are trying to do with the stairs but what you've done in that stair area is pretty complicated. Between the stairs, platforms, open stairwell, columns, the sunken and raised foundations and the tight space for the stairs in that area, something about that combination is keeping the stair base from showing. I could get the stair base to show with just the platform and stair when I placed it out in the yard by itself but couldn't get it to show inside. Bottom line is that I just couldn't find a way to get the base to show no matter what I tried. The best I can offer is a way to hide the open space under the stairs using half walls as shown in the pic below. I know it's not what you wanted, but it's the best I could come up with short of completely redoing that section of the build.
It's a beautiful build and I really like what you've done. It's obvious that you've spent a lot of time and effort on it. I'm sorry I couldn't find a way to get it to work the way you want it to.
Hope this helps.
