pfSense

First Scenario
When I create a Hyper-V VM selecting generation 2 as the hardware, pfsense will install but after install when it goes to boot it fails with an error about ZFS file system. If I choose UFS for the disk format it seems to work. Im using Windows 2016 for this test.

Second Scenario
When I create a Hyper-V VM selecting generation 2 as the hardware, pfsense will attempt to boot from the ISO and get stuck in and endless 5 second countdown cycle until the VM just powers off. Im using Windows 2012 R2 for this test.

I downloaded FreeBSD 12.2-RELEASE and ran through both scenarios above without any issues, so there appears to be some tweaks that you are doing to FreeBSD that is breaking Generation 2 Hyper-V machines. Here is a forum where users have found this same issue with version 2.4.5 of pfsense.
https://forum.netgate.com/topic/154360/gen2-pfsense-2-4-5-p1-elf64_loadimage-read-failed-windows-2012r2-hyper-v/8