I believe that I am having a similar problem with a Cadimage stairway in BIMx 17 (17.0002). It is a basic 7 3/4" rise x 10" tread stairway.
When I attempt to walk up the stairs I get stuck bumping against the first stair until I move up against the cable rail system that seems to allow me to slide upwards.
This is a file created entirely in Archicad17. The Cadimage stair is also created and modified in 17. However, if I save the Archicad 17 file as an Archicad 16 .PLN file, I can easily open the file in Archicad 16 and then "Export to BIMx". Strangely, in BIMx 16 (16.3827) the stair works perfectly.
In both BIMx 16 and 17, my camera radius was set at .25m. Increasing the radius to .40m has no effect.
I believe that this is a bug.