'Page not found' under live traffic not showing anything

Hi
Today I am seeing no stats under “Page not found” or “Top 404” tabs under Live Traffic option.

I even tried page not found manually from other system but not appearing under these tabs. It will never happen as there are many 404 per minutes for the traffic level we have.

see issue
http://screencast.com/t/cxLgm32uVay

https://wordpress.org/plugins/wordfence/