Why is only the small middle window not visible in the floor plan?

[LeeJaeYoung]

If you go down, it will appear in 2D again.

[Barry Kelly]

Check the Floor Plan Display of the window - symbolic, projected with overhead, etc.

It may be that it is above/below your Floor Plan Cutting Plane and the Floor Plan Display of the window will set if you can see it or not.

I generally have all my walls, doors and windows set as symbolic because I 99% of the time want to see them as being cut - unless I need to show them specifically as above or below the FPCP.

Barry.