OS would not boot without a monitor (headless)
Using the 7.1.2 version from August, the Pi 3 would not boot without a HDMI monitor attached. I worked around this by changing the overlay in config.txt to dtoverlay=vc4-fkms-v3d,cma-256 from dtoverlay=vc4-kms-v3d,cma-256. Note one version has an "f" fkms, and the other does not "kms". This allowed the Pi 3 to boot either with or without a monitor attached. Both overlays are in the overlay directory. Also through observation and through some web research, when these overlays are enabled, the HDMI parameters in config.txt have no effect. The "f" overlay has some display flickering issues when the mouse is moved, but otherwise seems usable. Still doing some testing, but am 99% at this time that the problem is solved. Just thought I'd pass this on for anyone having a similar issue. Hope it works for you, if you are having a similar problem. Thanks Igor for providing the evaluation version. Good luck with Emteria!