Question PCI x16 not working (Two Separate Mobos)

[theramman]

On two separate brand motherboards the x16 PCI Slot is intermittent (but mostly not working). Any GPU only works in the x8 slot in either.

System:
AMD 3700.
ASUS Crosshair VII X470.
32GB Gskill memory (2x16)
Corsair HX 850w.

I've tried my wife's 1070 in both slots and only the x8 works.
I've put my 1080 in the wife's pc and works fine.
I've tried different brands of GPU in the x16 and they only work in x8. I've had two cards in the pc and got to bios and it only shows a card in the x8 slot (see pictures below)
Updated both Mobos BIOS.
Cleaned my 1080ti contacts.

I had this issue when first assembled it originally but it went away except on the occasion but not working 99% of the time. Spent today installing the ASUS (original was a gigabyte x470) and same issue. It will show a picture 1 out of 20 times and after a reboot its gone. I can't even see the POST screen. If i have two GPUs in the current mother board I can get to the BIOS and it only will ghow the x8 card present.
Please any help would be appreciated, I'm at my wits end with a issue that makes no since and cant be narrowed down to one part or even possible issue.

https://imgur.com/yV1Psxa

View: https://imgur.com/yV1Psxa

https://imgur.com/N5urA4k

View: https://imgur.com/N5urA4k

https://imgur.com/NuEJmrC

View: https://imgur.com/NuEJmrC

 

[daltonjk]

Im having a similar issue with my GTX 1070, it only works in the pci x4 and i wont even get a boot out of the pci x16 on my old gigabyte board

 

[Calvin7]

Asus warns about updating Chipset drivers before flashing certain BIOS versions. There is more to it than just flashing the latest version.

 

[theramman]

Update: I hooked in another psu and it started working, I then plugged all of mine back in and it was still working. I put everything back together and it worked for a while but I restarted and boom back to no video.

I'm down to its the CPU... I've tried Two different brand mother boards with different GPUs and the PSU seems to will power everything in the x8 slot and when it works in the x16 slot. The CPU and GPU are the only constant variables and but PSU seems to power everything otherwise.