1) linux boot -> busybox: "No pool imported. Manually import the root pool."
zfs import -R /root $POOL
zfs import -d /dev/disk/by-id -R /root $POOL
exit

If still nagging about 'mount manually',
do each single 'zfs mount $POOL/dataset' 
even though they were already mounted.

Double check /etc/default/zfs