gptzfsboot unexpected results upgrading to 11.0-p2 from 11.0-p0

After years of reading, I made an account today to mention I ran into a problem with 11.0-RELEASE-p2 and ZFS root.

For background, during last week I went from 10.2 to 10.3 to 11.0-p0 successfully. However, going from 11.0-RELEASE-p0 to 11.0-RELEASE-p2 left me with the (common and generic) error of "gptzfsboot: No ZFS pools located, can't boot"

Copied directly from my terminal, I typed in this sequence:
freebsd-update fetch
freebsd-update install
zpool upgrade zroot
gpart bootcode -b /boot/pmbr -p /boot/gptzfsboot -i 1 mfid0

Unfortunately this particular computer is two-thirds of a continent away from me so I can't do much troubleshooting; I'm just stating I did have a problem. Hardware is an IBM x3550 and zroot lives on a passfile protected GELI volume, for what it's worth. Another machine, generic Asus/AMD/SATA, is fine after the same procedure to move from 11.0-p0 to p2.

My workaround was to boot remotely from an ISO of 11.0-p0, using "lsdev" following by "set currentdev=disk0" (from cd0) and "load /boot/loader.conf.local" before "boot" for the sake of anyone unfamiliar with booting a kernel from a different disk. (But that was late last night, my recollection might not be verbatim.)