11/22/'23 Added
While running HDMI compliance tests, I discovered that the real reason Guardband wasn't outputting was that it couldn't switch between HDMI and DVI.
Therefore, the Guardband output appears to be working properly.
I'm trying to modify the registry to switch the output mode after reading the EDID, but it's not working.
We are currently investigating this issue.
If you have an answer to this problem, please let us know.