It was definitely reproducible. First time that I got to that point, I rebooted. Second time, same thing, but by now I was Googling for answers on my phone and found the hint I liked to about doing ifconfig down and ifconfig up in another vconsole, and that worked.

Since then, and since I connected, it has not recurred, but I have only rebooted the machine into FreeBSD a few times since then.