Same experience for me. After installing on my desktop and laptop, I could see both machines in the app but I couldn't get it to work until I manually added the following rules to the windows firewall
%ProgramFiles%\Synergy\synergys.exe%ProgramFiles%\Synergy\synergyd.exe%ProgramFiles%\Synergy\synergyc.exe%ProgramFiles%\Synergy\synergy2.exe