hi, guys.

Both G1840 and G3260 belong to Haswell.

Also,
I looked into the details of HackFlags.

Unlike my expectation,
This option works to increase the limit register of "buffer size of enumerating PCI Express bridge devices"  from the initial value.

For example,
If you install an unusual number of video cards (like mining rig) with the default limit register value,
"PCIE device enumeration buffer" overflows due to too many PCIE devices,
Code12 exception seems to occur.

In addition to setting HackFlags,
disabling "some unnecessary PCIE devices" will reduce the occurrence of overflow.

Perhaps, Updating the "PCI Express root port" driver may also help you.
(ASRock H81 Pro BTC R2.0's "PCI Express root port" have more fit driver at WindowsUpdate named "intel(r) 8 series/c220 series pci express root port".)
Update: Sorry. Maybe this does not matter.

ty