Hello,
I was able to resolve the issue of the disappearing "3D DXF" model (DICAM V120405) inside AutoCAD with Tony at DNA (Thank you Tony). We opened a new AutoCAD document, using the "Aec arc (imperial).dwt" template and copy-pasted the 3D DXF drawing from the "problem document" into this new template. Now the drawing stopped disappearing into outer-space.
Alternately, I narrowed-in on the original problem. Comparing the exported documents ( version V180205 and V120405) in a text editor I had a hunch that the problem was somewhere in DICAMs "object-related-point(s)". This time I erased them all in DICAM, before I exported again with "3D DXF".
I opened this newly created 3D DXF document in AutoCAD and it now behaved properly. I could manipulate the drawing/model without loosing it in outer-space, and without pasting it into a AutoCAD template. Also, opening the exported 3D DXF in a text editor, all the "billion values" settled-down to 2-3 numbers before the decimal point.
Summarizing, DICAM's (V120405) 3D DXF export module creates billion values (10 numbers before the decimal point), when the DICAM model contains "object-related-point(s)". Exactly which object-related-points, I haven't figured out.