I have setup a process where I install the FirmwareUpdateStandalone.pkg on a computer and then Restore the High Sierra 10.13.2 image that I created with AutoDMG. Everything installs correctly, all of the APFS containers install correctly, the Macintosh HD, Preboot, and Recovery. You can boot to the Macintosh HD and the recovery and run the built in diagnostics, the only thing that does not see to work correctly is restarting or shutting down from the Macintosh HD. It dose not show you the gray spinning circle it just goes to a black screen and will sit there for a few moments and then restart or turn off. A same model computer that I installed from running the High Sierra installer, gives you the black screen with the gray spinning wheel. Not sure if this will be an issue, just strange.
Did you check if the Firmware is actually updated? Is this issue once or always? Once is 'normal' , for example, if you boot in Verbose mode, the shutdown will be in verbose mode too.
Reset NVRAM to clear any setting, and re-select Macintosh HD in Startup disk preference pane after first reboot.
The Firmware does seem to update and if I do not run the packager, the computer will not boot after restoring high Sierra to the drive and also the Boot ROM version gets updated after running the package. I have tried resetting the NVRAM did not see to make a difference. Re selecting the Macintosh HD did not seem to help ether. I even tried reinstalling macOS high Sierra from the installer and it does the same thing. Like I said everything seems to work fine it is just not showing the spinning wheel at shut down.