Your suggestion seemed very logical as it might explain the crash after the online update.
I removed the line in the configuration file and I also tried changing the line to designate "video" rather than "serial". Both gave the same result. Before the changes, the boot up stopped with a blank screen with a blinking cursor. After the changes, the boot up stopped with an alphanumeric graphic of the pfSense logo and a flashing cursor. The boot did not complete.
Since I am not seeing complaints from others, it looks like this is issue may be the result of a 10 year old bios in my Gigbox units. It appears that something is destroying the UEFI file when I do the configuration file restore.
I'll stick with bios. It will be interesting to see what happens during the next pfSense update.
Thanks for your suggestion and help.