Hi Guys,
I use ARD as well on my MAC pro's running Catalyst. They all run on 10.4.11 and with my macbook I can get hold of them always. No exceptions.
Maybe you have some options not enabled or disabled in the pref window for sharing, ARD settings.....
As I say. The configuration you mention works fine with me....
ARD 3.2.1 OS 10.4.11