Screentime works for Downtime, not for total App Limits

I use Screentime for control of my daughters Iphone. Downtime works perfectly, usage is blocked according to the time schedule restrictions I use. However, I also would like to limit the overall use of the iphone during a day, say 2 hours. However, if I assign 2 hours to "All apps and categories" in App limits, nothing happens (despite usage is blocked at the end of the limit), she can use the iphone as long as she wants (within the Downtime restrictions).

My iphone is Iphone 7, we both use IOS 12, and we both restarted our iphones.

What could be the explanation? And what would be a sollution? Thanks! Michiel