@aldobelus When you click on a Notification, #AndStatus opens Notification timeline at the last position that you viewed. This is by design. You need to scroll up to see newer activities.
As I see "Collapse duplicates" feature often hides several duplicated posts (activities) under one post, so if another duplicate was received, you see a Notification, but at a first glance it looks like no new activities were loaded.
I will think, how to improve this... Maybe highlight new activities somehow...