Only half of Tesla K80 works at a given time

Hello, I have installed a K80 (equipped with 2 huge fans) into a DELL Precision T3640 MT system (i9-10900K, 32G ram) and under recent Windows10 and latest NV drivers that identify themselves as (12/07/2021) only one of the GPU chips is okay. The second gpu is in Error 12 (resource problem), or when disabled/enabled in device manager, then I get Error 10.

When the working device is disabled in device manger, after few seconds, the non-working one comes alive and the error disappears!

Using nvidia-smi, I can identify the halves as being on bus 3 and bus 4, and running the Blackmagic RAW test, I get same 43 fps result on either of the halves.

Above 4G decoding is enabled in BIOS (otherwise none of the halves would work), and the BIOS was updated (to 2021/09 version).

I have tried to download the older NV drivers (difference is Cuda 11.4 to 11.2 in the dropdown boxes), but that version does not install, being incompatible with my OS, which is pretty strange when I dropdowned W10. While there can be multiple W10 builds, the NV driver picker does not differentiate between them…

So - what is wrong with the NV driver, that it does not enable both GPU’s that sit behind a PLX chip on a single K80 card?

Am I getting crypto-limited? (because there is an iGPU from the i9 cpu, so 3 GPU is a nono in 2021??)

I have a Davinci Resolve Studio license, which is said to support more then 1 GPU’s and the dusty K80 was the ideal candidate (12G of memory, and two instances).

I am willing to go for Linux, if that would work (Resolve works there, and I am getting references of better performance), but I would prefer to have this solved for W10 in first place. Thanks.