@geert.drijfhout welcome to the forum.
there is nothing you can do about it, this is how the Civil 3D API is designed.
You need to change the way you build the corridor: if two regions are contiguous and they have different assemblies, the first station of the region that follows will report the content of the last station of the region that precedes (therefore in your case is empty).
If the regions have a gap this issues does not occur.
My recommendation is to create a separate baseline per assembly.
In general is a bad idea to loft profiles all together because of how splines work.
You can do it only if you are absolutely certain that the cross-sections you loft will generate surfaces with the correct curvature (e.g. you might need to group the cross-sections).
Not all the geometry types are currently supported during the conversion from Dynamo to AutoCAD, you can export the geometry to SAT and import it back via AutoCAD (this is what is happening with the Object.ByGeometry() node for the solids).