ZFS not mount at boot

[beepc.ch]

Dear list,

I've freshly installed FreeBSD 13-RC5 following this wiki for ZFS manual 
configuration:

https://wiki.freebsd.org/RootOnZFS/GPTZFSBoot

After restart, the ZFS datasets aren't mount at boot:

# mount
zroot/ROOT/default on / (zfs, local, nfsv4acls)
devfs on /dev (devfs)

Doing a zfs mount -a, then everything is there:
zroot/ROOT/default on / (zfs, local, nfsv4acls)
devfs on /dev (devfs)
zroot/tmp on /tmp (zfs, local, nosuid, nfsv4acls)
zroot on /zroot (zfs, local, nfsv4acls)
zroot/var/log on /var/log (zfs, local, noexec, nosuid, nfsv4acls)
zroot/usr/ports on /usr/ports (zfs, local, nosuid, nfsv4acls)
zroot/usr/home on /usr/home (zfs, local, nfsv4acls)
zroot/var/mail on /var/mail (zfs, local, noexec, nosuid, nfsv4acls)
zroot/usr/src on /usr/src (zfs, local, noexec, nosuid, nfsv4acls)
zroot/var/crash on /var/crash (zfs, local, noexec, nosuid, nfsv4acls)
zroot/usr/obj on /usr/obj (zfs, local, nfsv4acls)
zroot/var/tmp on /var/tmp (zfs, local, nosuid, nfsv4acls)
zroot/var/audit on /var/audit (zfs, local, noexec, nosuid, nfsv4acls)
zroot/usr/ports/distfiles on /usr/ports/distfiles (zfs, local, noexec, 
nosuid, nfsv4acls)
zroot/usr/ports/packages on /usr/ports/packages (zfs, local, noexec, 
nosuid, nfsv4acls)

- in /boot/loader.conf
zfs_load="YES"

- in /etc/rc.conf:
zfs_enabled="YES"

I don't know what is missing.

Thanks.

xpetrl