Some motherboards disable power to their ethernet port upon sleep and so WoL will not work.
This is particularly common if the NIC is a power hungry 10GbE port.
However, in the particular case I found, the motherboard also disables oower to any usb GigE adapter attached.
The solution I found was to attach a USB hub with (empty) SD slots and integrated GigE port. As SD cards require power to remain mounted, the motherboard did not shutdown power to this adapter and WoL worked.
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