Is the HDMI cable touching or near the wireless antennas? I have seen scenarios where poor "cable shield " may cause this type of issues (radio-frequency interference, "cross-over effect... etc)...
This could be also due to poor shielding of the ports on the motherboards or internal circuitry... I don't think this is software issue but hardware issue since you can reproduce the problem connecting the HDMI cable and disconnecting the cable stops the issue....
What happens if you test other type of video ports? DVI, VGA, display port? If same issue, and you already tried high quality HDMI cable avoiding touching or hanging near the antennas, I would say this is a hardware problem ( I don't know if with the cable, antenna, motherboard ports) and you want to review it with the mobo or cable vendor...
I see you have tested some different cables, but make sure they are not "cheap" cables but high-quality certified HDMI cables with better shielding. I saw one post here (couldn't find it) where a user had a similar issue and he solved replacing the cable and using a tie to avoid the cable touching the antennas...
If you search the Internet, you may see many post of issues like this one but with different devices...
Megan ❤
