I think the problem in your second post has nothing to do with ARCHICAD or the GS-AC Connection as it doesn't happen in any of the ARCHICAD Nodes of Grasshopper, seems like a purely Grasshopper bug. (works on Windows for me).
About the first question in this thread: Does Grasshopper segment the Wall into little segments. What does the data coming out of that Node show? Does it show one line of data for that curved Wall piece or does it show many?
If Grasshopper does it there may be a way to preserve the curved geometry (I don't know for sure). If ARCHICAD does it then it may be a bug in the GS-AC Connection.
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