There are a couple of things you may want to check. The first is that you have an opening in your floor above and that it is visible in your view. The other thing is the Floor Plan display settings of your stair.
Here is a quick sample wherein I inserted a stair, created an opening (shorter than the full run stair as you noted) and adjusted the Floor Plan display settings for both the Relevant Story and Above Relevant Story. I did not make other improvements (e.g., solid outline of slab opening, rails, etc.), but just to give the basic idea 'out-of-the-box'.
I hope this helps.
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