I’m guessing this is a new town line from EF to Storybrook Maine. Once Little John is dropped on the other side of the line, he will forget he ever saw the monkey. And he will have forgotten all of the past year as have everyone else who’s crossed the line.
Its also possible that many were cursed to return to storybrooke, and have no memory of the past year, but possibly others, like Little John cross after the curse and maybe they still have their memories intact?