ORIGINAL: StrutNtom
Here in SC this "lull" is easy to solve.
October is when our white oaks start dropping their acorns. Find the white oaks and you will find deer. I see more deer in October than any other month because I hunt the white oaks.
I think this is the answer also. The deer don't have far to go from bedding to find the acorns so they don't move much. And the guys waiting for them on the edge of the fields don't see them, so they figure they dissapeared. They're around, they just found a new food source.
Another answer might be, they got bumped off of their regular rutines by the mass invasion of bowhunters into the woods. If you suddenly had a bunch of strangers walking around in your backyard, you might avoid it too.