@Rahul-Balaggan one more theory if it helps: the threads I see in "unread" are all because i am subscribed to a topic - bookworm. In this topic I see all new threads with new posts in my unread section, even if I am not watching individual threads - ex. I wasn't watching manga p3 v7 but I still saw it listed.
If I am just watching individual threads, I get notifications but do not see them on the "unread" section.