I have a Crosshair VIII Extreme. The PCI-E_1 Speed was first working fine with 16x4.0 Speed. After a few days i bootet up the Pc and the Bootup took longer then usual. Then Before the BIOS ROG Logo Screen the Message appeared "PCI_1 Speed was set to 8x".
Since that i can not manage to run the Graphics Card to 16x Speed. Even if i set Everything on 3.0, 4.0 or Auto.
The Settings in the "CPU PCIE Configuration Mode" is set to "PCIEx16_1+M.2_2+M.2_3". I didnt even install a M2 in M.2_2 and M.2_3. I only have an M.2 in M.2_1 and in the Dimm2.Modul.
What i tried so far:
Doing a CMOS reset,
Installing a fresh new BIOS (0504),
Reinstalling Chipsetdrivers (184.108.40.2066),
DDU uninstalling the Nvidia drivers and reinstalling the GPU driver again.
New Windows 11 installation (Win 11 V. 22000.493)
I tried out an other Graphics card (3070) - same error, only PCI8x avaliable
Then i changed the Mainboard to my other x570 - there everything works fine with 16x4.0
You cant use cpu pcie config mode: "PCIEx16_1+M.2_2+M.2_3 its revert to 8x mode so m2_2 and m2_3 slot cant be used in this motherboard if you want to have 16x mode. I know its a stupid flaw in this board and you can only use m2_1 slot and the dim2 module. For a high end board its a bad decision from asus.