Just went to my board for the first time this morning.

I click on "New content" and it says "There's nothing here yet".

I have these 3 filters checked:

But when I look at my board there is clearly new stuff and I have email notifications about new replies.

What's wrong?

Change your time period from "my last visit" to the entire day or longer. The content may not have been "read" by you, but it may be older than your last visit to the board.

That's not possible because I use "New content" several times a day and after going through them I always click "Mark board as read".