This notification just took me to the top of the page in that thread, and the last entry is not separated from the old posts with the "new posts" separator. So unless you look at the timestamp of the post you won't, easily, recognize what you have not read.
https://ultimaker.com/forwardnotification/168478
My notification said there were 4 unread and took me to the top of page 50, when I got to page 51 there was no line separating read from un-read.
https://ultimaker.com/forwardnotification/37370
Got a notification for one unread post but the other details are the very same as for @peetersm