GEOM has amnesia

Hi I brought this up earlier, but didn't have as
much to go on as I do now. So I'd like to try this again;
On a recent(ish) install of CURRENT followed by a new
kernel/world. I'm finding I can't depend on geom(8) for
anything, but the primary (SATA3) drive, it's installed on
(if even that). To the point;
Blanking/partitioning/formatting a usb memstick to to
dump(8) this system to, works fine *until* I reboot.
Where I'm greeted with
GEOM: da0: the secondary secondary GPT table is corrupt or invalid
..
GEOM: diskid/DISK-... : the secondary GTP table is corrupt or invalid
..
using the primary only --

gpart recover returns the status to OK, *until* I reboot. Where
I'm greeted by the same BS.
OK I can't live with this, so I grab a usb2 external drive off
the shelf, and try it again. blank/partition/newfs && fsck
mounted the partitions on /mnt and performed a restore.

Reboot; && get the corrupt GPT message.

So. I spin up an old 11 server I have sitting in the closet, with
this external drive attached to it. I do *NOT* get the corrupt GPT
message. So I blank/partition/newfs the external drive &&
mount the partitions individually to /mnt && restore again. When I
reboot to the external drive still connected to the old 11 server,
I do *NOT* receive the corrupt GPT message. WooHoo! I think.
So I re-attach the drive to the new 12 server. Reboot, and can't
boot to it && get the corrupt GPT message.

GEOM seems to be broken in 12, maybe even (recent) 11. As the 11
server I used for testing is ~9 mos out.

What can I do to (help?) fix this mess?

--Chris

See also: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=218026

Thanks!