Found these threads related to your problem:
I tried to install Freebsd 12.0 RC3 and got the same error as mentioned here: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=233098 Also on a amd64 box. "Startup error in /boot/lua/loader.lua: LUA ERROR: Cannot open /boot/lua/loader.lua: no such file or directory" "can't load kernel" Is...
forums.freebsd.org
I have burned at least 6 DVDs of the ISO FreeBSD-12.1-RELEASE-amd64-dvd1.iso, using every iteration of method I can find, and attempting to boot from any of them BEGINS the boot process, but terminates with "?" and "...BOOT\LUA\LOADER.LUA not found", yet examining the distro finds that file and...
forums.freebsd.org
There is one comment that may fix your issue, but I am not sure of that at all, so be careful, read the entire thread before doing anything and look also at the bug reports:
running into the same problem here. Thinkpad X1 Carbon 5th gen, currently with Arch Linux on it. Tried -CURRENT, 12-STABLE, -RELEASE memsticks and disc1s, none worked and all gave me the same error.
forums.freebsd.org
Side note, your server is on 13.0-RELEASE, it's out of date, 13.3 is the last one.