What mother board you are using??
I had similar sort of issue with my Z270P board which adding up my 5th GTX 1060 card, i've fiddled around a lot and struggled a lot with Windows.
Then I've switched to Linux (Ubuntu), problem seems gone away.
But it was a long time ago (10 months seems very long to me now
), I do remember playing with BIOS settings too.
I would suggest to check the BIOS settings on your mobo and enable 4G or similar option.
Hope it helps, good luck