I have a Z270 MoBo too, however built by MSI, with the I219-V NIC chipset, and I too got a wireless PCIe card built by Gigabyte, however with an AC 8260. I had zero issues during setup or utilization for the past month or so, with any drivers, until I updated the Intel ME drivers (which has absolutely nothing to do with network), and this new driver broke the ANS feature of the NIC. Was I not using VLANs, I would not even notice the problem.
I usually download all drivers for my system and save them anywhere I can have access to, then install the chipset, RST storage, wired Ethernet, wireless Ethernet, Bluetooth, onboard graphics, discrete graphics, audio drivers, then a round or two (or three) of Windows Updates, to finally start with the programs. So far, never had any troubles using this order.
I would report your findings back to Asus, even if only as a link to this topic. However after almost 20 years of using Asus products, I can tell their product quality dropped significantly (from MoBos to VGAs and laptops, to name a few). I would still purchase from them, but not as my first or second choices.