Thanks for using ArcGIS for AutoCAD!
Off hand I cannot think of anything that would cause this behavior nor have I seen it in testing.
1) What vertical (basic AutoCAD, Civil 3D) if any of AutocAD are we using?
1.1) What version of AutoCAD are we using?
2) Is this feature layer a hosted layer or a feature service referencing data from an enterprise geodatabase?
3) You mention lines (force main) are added as expected. What are the other lines that are not being added?
3.1) Are these other lines on another sub-layer?
3.2) Is there any difference with the force main lines versus the lines not being added?
4) Can someone check the ArcGIS Server logs right after you add this feature layer to your drawing?