QUESTION:

When I import a 2D DXF file, why is some of the geometry missing.

ANSWER:

This is probably because the geometry is made up of block objects. If this is the case, simply explode the block(s) in AutoCAD and re-create the DXF file. For some blocks-within-blocks, you may need to explode them a couple of times.

For more details on Importing CAD geometry into ECOTECT, have a look at the tutorial "Importing CAD Geometry - 3DS & DXF files" that comes with ECOTECT.