TL;DR the “bug” category shows “1 new” but when I go there, there is nothing to see.
First I thought this was a sidebar issue but I guess I have discovered it because the sidebar shows per-category “New” counts.
Maybe this is happening because of the fact that the latest topic has been closed already?
Addition: this was a self-solving bug report, when I made this topic the problem went away 
I have certainly seen this before, but its a hard one, we need to figure out a repro.
I have seen this when I created a new sub-category. There is always this “About [Category]” topic, which is kind of semi-visible.
I have the main category in the sidebar. After creating the subcategory, the sidebar showed “1 new”. I clicked on it, showed the main category list and – nothing in it. As I realised what I have just done, I went into the subcategory, clicked on the “about” topic and the notification went off.
I don’t think this is your case but maybe it will help.
I am also having this issue!
Sometimes it shows “New (7)” but I only have one new topic; see images:
I also have this issue with “Unread” also:
Forum Link: https://forums.flightsimulator.com/
