I got a category which show 5 discusions in the categories listing.
But when I click on it I can only see 4 discussions.
How is it possible ?
I can't answer the "How is it possible", but I can answer the "how do I solve it":
You visit [your forum URL]/dba/counts .
Too bad ! It does not work for me.
Do you have access to the database? I would take a look in gdn_discussion to see if there's a discussion entry there that matches that category but that you don't see on your forum.
Can you run a database query like e.g.
WHERE CategoryID = X
where "X" is the ID of that category.
That should show 5 discussions and should give a hint on the "missing" discussion.