1) Open Monitoring -> Overview page and make sure you see some data or triggers there.
2) In Administration -> General set option "Dropdown first entry" to "none".
3) Open Monitoring -> Overview page again. At first nothing is displayed. Select a group. And nothing is displayed. Try to filter something, but nothing is displayed.
Possibly broken in r45904. There is quite a difference. In 2.4 there is simple code
But in 2.2 there is more logic when data should be displayed: