If the app isn't running and I get a notification when I tap it I get the notification feed, but I can't press back to exit the app or close the notifications.
Oh boy, that was a bad one! It was not just that coming in from a push notification was blocking leaving but that having the notifications panel opened at all blocked the back button's press due to some over eager logic in the implementation of the
DrawerLayout from Google.
This is fixed and will go out in the next app update, thanks!