I modeled my first two parts, and I also think I know what is wrong with the AHC-03 (Hexagonal Hub) model. I modeled my own AHC-03 and ASB-18 parts and with my models I can attach a part to all six faces of the AHC-03 without any problem.
I believe the problem is in the dimensions of the faces of the AHC-03. I used a 1.1" square dimension on the sides and it worked out fine, so I think increasing the face dimensions slightly will correct the AHC-03 problem. I am going to see how close I can cut the face dimension before it causes a problem.
I suspect a dimension problem with the ASB-19/HUB-09 also.
8-Dale