[xxpor]

I have a similar issue with a Nvidia 1080Ti on my old desktop. It's related to the UEFI deciding if the iGPU or the Nvidia GPU should be primary and to disable the iGPU or if the iGPU should stay enabled.

[hiatus]

Curious how you went about determining that was the source of the issue.

[xxpor]

I'd swap the cables around and could see video from the iGPU output.

[josephg]

If this is the problem, you can usually force the GPU choice one way or another in BIOS.