I have exactly this issue. My desktop PC (Windows 10 64bit Pro) is connected to my router per ethernet and my smart phone (Samsung S4 running Android 5.0.1 Lolipop) is connected per WiFi. Action RCU does not find desktop PC: "No computers are available".
It is very unnerving that apparently no official answer was ever made to this thread. The only reason I am attempting to use Action RCU because I cannot get Action to record Steam games normally by starting recording through the hotkey