I have this pretty Maximus X Hero (Wi-Fi AC) motherboard paired with my Gigabyte Aorus GeForce GTX 1080Ti Xtreme Edition 11G.
The card is in the 1st PCIe slot and both parts support PCIe 3.0 speeds of x16.
The problem is that the card is stuck at x2 PCIe speeds and refuses to work at x16.

Even before hitting Windows and just checking it in the bios, it says that the slot is running at x2 native, not x16.
The Windows install is fresh, latest drivers, and since the Bios already told me about this x2 limit I feel it's safe to assume it's not (Windows) software related.
In Windows in CPUz it says the same, running at x2 only, but x16 capable.
Stressing the system with a game/benchmark doesn't up the PCIe speed (so no powersave mode afaics)
The motherboard ran bios 802, 1003 and 1101, all the same problem.
I have not tried different videocard bioses yet as there are no updates available and trying non official bioses might kill something besides my warranty.

I've reproduced this error/feature/bug on 2 of the same X Hero motherboards, so unless they're both identically broken it is not a hardware fault in the motherboard.
The videocard is fine, running at x16 in other motherboards and even x8 in the secondary PCIe slot on the Maximus X Hero, it's just stuck at x2 in the primary slot on this type of motherboard...

I don't like running it in the secondary slot due to very restricted airflow, plus it's a brand new motherboard, it shouldn't be like this.

Can anybody shed some light on this?


There is one more bit of odd behavior:
I wanted to test the primary PCIe slot with some backup videocards and found they didn't give any picture.
An old GT220 and Asus ENGTX560 both didn't give a picture in the primary slot. But they worked in the secondary slot.
When I added both cards and checked the bios with the card in the secondary slot it said there was no card in the primary slot at all.
I didn't fidget with any of the PCIe settings, all vanilla.