It sounds like you don't have above 4G decoding enabled.  Verify it's on advanced - system agent (sa) configuration - above 4G decoding in bios.  Updating the drivers is probably a good idea as well for LAN, Chipset, SATA, and VGA.

https://www.asus.com/us/Motherboards/PRIME-Z270-P/HelpDesk_Download/