Did you check the PCI latency?  Needs to be set at 96.

Check this out, might help with the BIOS settings:

https://blockoperations.com/configuring-bios-settings-gpu-mining-intel-motherboards/


I just built my rig about a month ago with that board and it's given me all sorts of headaches.  I've had the system lock up and the BIOS settings reset.  Reset CMOS, replaced the battery, and still happens on occasion on hard reboots.  When the system shuts down properly it's no problem, but when one or more cards become unresponsive, it can hard lock up.  I'm using Claymore's miner and uses the flag to reboot when there's issues with a GPU but it will still lock up on occasion.