Have you done this to try to stop Windows Update ?
Maybe you already did that, but it has worked for me.
run services.msc
Scroll down to Windows Update.
If its shows running, right click and select STOP.
Then right click again and select Properties.
Set Startup Type to Disabled.
Exit the Services Menu.
Reboot.
Then check again to be sure its really disabled.
Actually I have done that about 4 months ago. It's currently set to "manual", so I must have either not applied this tweak properly, or it somehow mysteriously switched. Thanks for the reminder - I have gone ahead and disabled it.
Additionally, thanks to you I tried using a 4-port HDMI switcher that I had laying around to see if it would give me the same result as those dummy plugs you spoke of - and it has indeed solved my problem

Cheers!