I recently rode the Norton Summit segment on the climb portal and it’s quite badly wrong particularly between gate 4 and 3. I’m a local to the Adelaide area with over 100 ascents of the climb and I can say categorically that there are no downhill sections mid climb and absolutely no sustained 13% sections.
It looks like velo viewer is the source of the issue
There appear to be a couple of versions of the climb on velo viewer. The one with the very consistent gradient is more correct looking than the one used in game.