Você precisa mover a declaração de hosts para fora da declaração de sub-rede:
subnet6 2001:470:1f1b:5b3::/64 {
range6 2001:470:1f1b:5b3::1000 2001:470:1f1b:5b3::ffff;
range6 2001:470:1f1b:5b3::/64 temporary;
option dhcp6.name-servers 2001:470:1f1b:5b3::20,2001:4860:4860::8888,2001:4860:4860::8844;
option dhcp6.domain-search "patrikx3.tk","corifeus.tk";
}
host linksys {
host-identifier option dhcp6.client-id 00:02:03:09:05:05:60:38:E0:10:A7:EB;
fixed-address6 2001:470:1f1b:5b3::1;
}
...