It looks like wake on lan is broken on iPhone X.
On my iPad Air 2 it works but take 40s to start the PC.
With a little tool named « wake » by Dave Thompson the PC is powered on instantly on iPad and iPhone !
The wake on lan is still not functional on iPhone X and it tooks more 40 seconds to work on iPad Air 2 on 5.6.4
Both with iOS updated to 11.2.1 version.
Not tested on Apple TV.
As iOS 11 prevent apps to get the MAC address in the arp table, I think you have to add a setting for enter the MAC address manually.
This is why it doesn’t work on my iPhone X and Apple TV 4K.
It’s still functional on my iPad because the MAC address must be saved by infuse before I upgraded it to iOS 11.
But it does not explain why it takes 40 seconds to power on the PC.