To do this I needed more ethernet ports, so I bought a 4xLAN FACE module.
After installing the 4xLAN FACE module, the Fit-PC3 would not boot or display anything.
USB ports had power, but other than that it did nothing.
Checked the 4xLAN FACE module for damage or other obvious problems, but found none.
Tried reseating the 4xLAN FACE module, which had no effect.
Removed the FACE module and noticed that the machine started normally.
Mounted the original 4xUSB FACE module and the machine also started normally.
Reseated the 4xLAN FACE module multiple times, but the Fit-PC3 still didn’t work.
Removed the FACE module again.
Examined the BIOS version, which was 18.104.22.1683_7
Checked the latest BIOS version and noticed a long list of changes.
Upgraded to BIOS version 22.214.171.1243_14
Mounted the 4xLAN FACE module and the Fit-PC3 could now boot and display normally!
It’s unknown to me which BIOS version fixed the problem, but one of them did.
The latest BIOS versions add a lot of options, so that alone makes it relevant to update.
The bottom line is: Update a Fit-PC3 to the latest BIOS version before installing a FACE module to avoid potential problems.