This is a well known limitation of the stair tool.
The devs chose the easy way and decided that if the stringer is too "hard" to calculate to just not do it at all.
Of course there is a way and this stair is far from unbuildable (real life).
But, as you can see with the left stringers: even they wouldn't look like that in real life. No carpenter would do it like that.
Funnily enough the method chosen for the construction of the minimum height body is almost always better suited than the actual implementation for the stringers.
My recommendation is to disable the stringers and building them yourself (with the methods a carpenter would).