I just updated my z270x Intel (Gigabyte) Motherboard. I upped the BIOS from F6 to F7, fixing a hyperthreading fault. Afterwards, my wifi chip didn't work.
There has been some discussion on the Arch Linux Forum that claims you have to turn off the PC completely for a sufficient amount of time so the card can completely shut off and reconfigure itself for the new BIOS.
That doesn't work for me however (5min wait without power cord attached and pushing power button a few times)
Odd is, the bluetooth (which is on the same adapter) works.
What did help me in the end was placing the PCI adapter into a different slot. It might be, that this finally allowed the card to discharge or it could have some other effect OS. But placing it from PCI slot 1 to 6 solved it for me.
So: BIOS Upgrade? Move the Wifi Adapter a bit.