To add to this, I was there the first weekend in October after Phase one opened and FJ had about an hour long line, the shops were bearable for a quick look around, The Three Broomsticks was at about a 45 minute wait at 1pm, and the Ollivander's line was an hour (that got skipped). The rest of the park was pretty dead but that area was hopping.
I would say it was due to HHN, but most of the guests in the HP area were from the UK and Ireland. Do expect some extra crowds due to HHN and shorter park hours on your trip.