I was trying out the Center Position in the ATC today. It was all going well. However, I am not able to contact some aircraft.
For example, I heard one aircraft calling to me for request to descend via a STAR. However, the aircraft that called me was not on the map or the list of aircraft on frequency. He called me multiple times, but I was not able to respond. Also, not every aircraft in the Center coverage is showing up on the map.
Is this an issue, and is it already known? Or is it supposed to be like this?