Hang on /sbin/init

Hello all,

I've been running a Raspberry Pi (8GB) since FreeBSD 13 was released.
I'm running ZFS on root with three mirrored USB drives.  It's been
working fine for months.

A few days ago the system hung overnight; the screen was as I left it
but the keyboard and network were unresponsive so I power cycled it.
It won't complete the boot process.  When I boot in "verbose" mode,
I see messages that seem normal to me. The last message I see is:
"start_init: trying /sbin/init".

The keyboard is responsive -- I can use scroll-lock to look at old
messages and I can use alt-ctrl-delete to (try to) reboot.  Network
is not responsive.

I've mounted my ZFS pool on another system and it seems like it's OK.

SO, I'm unsure how to proceed.  I have backups so I can rebuild, I'd
really like to recover my system,

Help?  Advice?  Suggestions?