Try reconnecting to your WIFI network.
I apologize I don't quite understand your advice. In this case, there are 3 computer involved: ControlPC, AudioPC, and my laptop. I usually try to control both ControlPC and AudioPC using my laptop with Splashtop.
ControlPC and AudioPC are both wired LAN connected to a router, while laptop is connected through Wifi.
The problem is when AudioPC wakes up from hibernation, my laptop can of course still see ControlPC through Splashtop, but my laptop fails to see AudioPC through Splashtop.
I hope my wordy explanation is clear enough to describe the symptom.