The issue is that UIApplication doesn't fire a notification when an app has become inactive, but it tells you when it will become inactive (did vs. will). As a result (it's clear once you read through the code), the native portion of the AppStateIOS module never tells JS when the app has become inactive.

This should be reasonably easy to build as long as the state tracking is kept simple. It's not super urgent but would be good to get in before a lot of people start assuming "active" and "background" are the only two app states.