Blocking some streaming radio via Web Protection, Application Control Rules makes no effect

Hello,

My goal was to block some live radio streaming traffic for all users. In particular, I was hunting after the ShoutCast.

First, in the Flow Monitor, I noticed, this ShoutCast is being continuously used all days long. So, I clicked the button to block it. Confirmation message came up and a new rule was created in Web Protection, Application Control Rules:

This had no effect. Then, I added another rule to block any "Streaming Media" and "Streaming Media and Messaging" with Productivity <= 1 and Risk <= 5 (this would still allow YouTube):

This also had no effect. I can still see that some users are streaming the radio from the ShoutCast.

My UTM is 9.506-2
Web Filtering is enabled, Mode is transparent; HTTPS Scan Settings are URL filtering only.
There are several profiles configured for different groups of computers to allow/block Internet access for specific periods of time. Everything works as expected. So, my media streaming condition I want to apply additionally to URL filtering only for those groups who is allowed to general Internet at that time.

Am I missing something? I would appreciate any advise.