This quick-and-dirty fix seems to work for me:
root@odin:~# systemctl cat nfs-kernel-server
# /lib/systemd/system/nfs-server.service
[...]
# /etc/systemd/system/nfs-server.service.d/zfsutils-linux.conf
# If you configure NFS exports in "zfs set sharenfs",
# this will remove all your NFS shares!
#
# systemctl stop nfs-kernel-server
# systemctl start nfs-kernel-server
#
# This is an attempt at a quick fix.
[Service]
ExecStartPost=/sbin/zfs share -a
