Why this move has been made and when/if we will see the Are You Afraid of the Dark? movie is unclear, but Paramount didn’t say it was cancelled, so there’s hope.
Paramount didn’t announce that Are You Afraid of the Dark? has been delayed until next year or a new release date for the film, simply that it is unset.
As far as that October 4 weekend goes, Joker and The Woman in the Window are still set to open then.
That means that the next meeting of the Midnight Society won’t be happening in 2019.