gplea: I don't have a TV/monitor in this setup. It's actually an old 15" IBM, with 4:3 aspect ratio connected to my laptop which IS 16:9.

This sounds like what I was referring to, your monitor...

I think I have figured this out, at least for my Windows 10 PC: My monitor (really a 1080p TV) takes some 5-10 seconds to boot,* during which time the PC is not detecting monitor information about...

I have had this same problem on several machines with Windows 10 back thru 7. It seems to be a Windows bug, in my opinion. And no, my arrangement settings aren't wrong.