Cannot create 360° spiral staircase

[eidam655]

Hi!
I am trying to create a spiral staircase that ends on the same line as it begins (so a full 360° circle).

However, even though my Archicad draws the preview successfully, it doesn't create any geometry. 

Is there no way of doing this as one object? Does Archicad read the same start and end vertex as overlapping?

Thanks for any answers!

Operating system used: Windows 11 24H2

[Erwin Edel]

It also managed to draw coherent stringers instead of fragmented twisted up polygons pretending to be a stringer.

[Lingwisyer]

I moved the stair objects and rail objects from pre-AC21 to an external library as soon as many of the limitations came to light. Rarely use them, but it's nice to have.