did you try the install with nothing but bare minimum? So no nics, only one hdd presented to the guest (just for the c drive), usb 2 only.
Nothing different about the iso, so nothing slipstreamed in?
If you clone one of the working machines, then do a sys prep on it (so treats it like a new install) does this work?
I'm going to be offline for a few days, so may not respond right away.
Some of us had to hide our services behind vpn. As the last time I had my webserver exposed for to have others see my test site (I test internally before moving to public servers) I was dropping over 5000 connections a second that was trying to login to my page.
So my little server was getting hammered, and my other traffic started to get effected.
So you might be fine, others might have constraints that are not common.
YEs I agree the screen should be turned off, but that can be a software thing. As the screen on ubuntu server by default powers down after a few minutes anyway.
Some laptops vent heat out the keyboard, so closing the lid can trap heat. OP check how warm the keyboard is after being on for a while. You don't even have to have the screen open all the way, just a little bit (10 degrees) to allow the heat to get out.