Hi, hopefully this is a simple issue. Reading your post, I'm inferring because you have to "pull out a monitor to keep troubleshooting this machine" means that in normal operations, there is no monitor plugged into the video port, is this correct?
Second question is, are you using the on-board video, as opposed to a discrete graphics card?
If the answer is yes to the questions, AMT will see the video channel as closed when there is nothing plugged into it.
You will need to make a purchase for headless operation, something like:
https://www.amazon.com/CompuLab-fit-Headless-Display-Emulator/dp/B00FLZXGJ6/ref=sr_1_3?ie=UTF8&qid=1511902526&sr=8-3&keywords=headless+hdmi
Or DP or VGA depending on your video connector type.
This is also assuming you are using the onboard video and not a discreet video card, otherwise, KVM will not work.
Let me know if this helps.
Regards,
Michael