I am getting a crash on Rhino 7 when running DupMeshEdge on a SubD object. I have tried it several times and it is consistent. It allows me to select the edge then never completes. Please let me know when you get a chance if this is my system or a bug.
Sorry did not answer the second part of your question. Does not seem to mater what edge I pick here. I also created a simple object to see if it was specific to the geometry and it happens on both.