Same problem here: - I'm building FreeBSD head on a builder machine, and NFS mounting its /usr/src and /usr/obj to 4 others
Results: - 2 of them, UEFI+ZFS machines works great ((Thinkpad T420 and AMD Epyc with Tyan motherboard) - 2 of them, BIOS+UFS machines meet this "can't find /boot/ua/loader.lua" (HP microserver and PC Engines APU2) I had to boot from an USB stick, mounting the system partition and "cp boot/loader_4th.old boot/loader".
