In section views, center lines of geometry elements may not be displayed automatically. In this case it is necessary to insert them manually.
Open the specification bg_scooter_dwg and switch to drawing mode.
To insert centerlines, in the menu Centerline, under Insert -> Centerline (see figure "Centerline Dropdown") there are the three following important functions:
Center Mark
3D Centerline
2D Centerline
Select the function 3D Centerline and mark the front sides of the respective shaft.
Your drawing should now look like the following figure (see figure "Centerlines").