All geometry must reside on the Default Layer 0 in SketchUp.
And like Anssi says, SU cannot recognize AutoCAD Architecture walls and other ‘proprietary’ objects.
You might try breaking up the original file into a set of smaller, properly prepared files.
That is, export to AutoCAD certain layers from the original CAD file to separate files for import into SU.
Therein, reassign all geometry to Layer 0 prior to import into SU.
Bring into SketchUp only what you need and in a form it can recognize.
Delete and purge all else from the CAD files prior to import into SU.
Unlike the image below…
A properly prepared CAD file will indicate no AutoCAD Entities Ignored in the Import Results.