IB Market scanner: "No items retrieved"

I created a "Market scanner" page in IB's TWS. It works fine during market hours, but after hours (like now) I often get a yellow line saying "no items retrieved" instead of the scan results, regardless which parameters I choose. Is that normal?

 

Dude that's a RT scanner. Wait for the market to open.

 

I know it works in real-time, but why would that prevent it from working after hours?

In fact I've used it after-hours many times: sometimes it works, sometimes it doesn't.

I contacted IB a week ago about this problem through chat. They weren't able to solve it or explain what the problem was, but they certainly didn't say it was b/c the scanner was designed to work only in real-time.

 

AFAIK, it will only generate results during market hours. I've never seen any output after the close.