ZFS USB Stick - not portable?

[Peter Pauly]

I installed FreeBSD-11 to a USB stick with GPT and a ZFS root file system
and GELI encryption. I can boot it fine on the original system, but when I
tried it on another PC, it boots the kernel, but can't mount root:

Cannot find the pool label for zroot
Mounting from zfs:zroot/ROOT/default failed with error 5.

USB drive is da0:

I remember from back in the day that it was necessary to do an export each
time before mounting it to a new system. Is that my problem? Should I be
able to move between systems without any special action?