M.2 slot PCIe not working

[azzurro]

Hi,

i've got this motherboard click but the x1 M.2 slot unfortunately doesn't seem to recognize any PCIe peripherals. A Samsung Evo 970 Evo as well as an Optane P1600X work flawlessly though.
It has been hinted to me that the BIOS might not be looking at PCIe devices during enumeration.

Would this be something that could be modded in?

Thanks!

[azzurro]

I have to update this. "doesn't seem to recognize any PCIe peripherals" is greatly exaggerated. It seems, that only a ASM1166 NVMe M.2 card or even the ASM1166 PCIe card (using a M.2 to PCI riser adapter), which normally works in this board in its PCIe slot, isn't recognized.
I've tested several NICs (I226V M.2, Intel 82599 10G adapter via M.2 to PCIe riser adapter) and even some random, old LSI SAS HBA. All work.

The ASM1166 doesn't though, although the cards are known to work either in the very same mainboard's PCIe slot or in different mainboard's M.2 slots respectively. The board currently has one ASM1166 onboard and one connected via PCIe to it.

Connecting the working one, which is in the PCIe slot, through the M.2 to PCIe riser adapter instead, doesn't work either. So it apparently isn't any conflict, it is just the M.2 slot not liking the ASM1166 specifically, for whatever reason.
I have not enough deep knowledge to be able to even guess the reason for this.

I'd massively appreciate any help.

Thanks!