It seems like there is a limit of 18 connections when creating custom MEP parts. I was modeling manifolds for PEX plumbing systems. The manifold systems typical range from 14 to 36 ports, plus an additional 3 ports for supply and through connections.
I reviewed the GDL code and it seems to be limited to 18, which seems reasonable for most objects. That limit would need to be expanded to 40 to accommodate the largest manifold.
Regards,
Joe Augustine
ArchiCAD 20
(since 8.0)