I was successfully able to use the RPi UEFI 1.14 firmware release to
boot a Raspberry Pi 4B 8GB model when disabling the 3 GB limit. I was
also able to reboot successfully (several times) after initial booting.
I did not use the HEAD/latest image because it seemed to point to an
older release (from 3rd June). Your NetBSD identifies as "NetBSD
9.99.64 (GENERIC64) #0: Wed Jun 3 07:06:18 UTC 2020" whereas mine is
later: "NetBSD 9.99.65 (GENERIC64) #0: Mon Jun 8 22:52:09 UTC 2020".
Maybe a later image might work for you, too?