Wake-on-LAN behaviour changed from Windows 7 to Windows 8, 8.1 and 10, preventing the zero client from waking the host PC if the zero client was configured to send the WoL packet to the host PC NIC and not the remote workstation card. Windows 8, 8.1 and 10 will not wake up the host from an S5 (power off) state when it's NIC receives a WoL packet.
Windows 7 can wake up when receiving the WoL packet. (See https://support.microsoft.com/en-us/help/2776718/wake-on-lan-wol-behavior-in-windows-8-windows-8-1-and-windows-10 for more information)
To get WoL working again, reconfigure the zero client to send the WoL packet to the PCoIP remote workstation card.