Update: saw a new update, 22.05.b.20220524.1701, and tried to update from the console. Except for the strange ZFS errors, everything was fine until this happened:
pkg-static: Not enough space in /var/cache/pkg, needed 111 MiB available 106 MiB
I increased the ram disk for /var from 256MB to 384MB and rebooted.
No warning about /var not having enough space, but the update did not happen.
Increased the ram disk for /var to 512MB and rebooted. Again, the update failed.
Disabled the ram disk and rebooted.
Success! Until further notice, I am not using a ram disk for /tmp and /var.