vyos generates host-identifier option with excess quotes, causing the static host declarations to not work, clients get addresses from the dynamic pool instead. isc-dhcpd shows no error.
Vyos-generated non-working /etc/dhcp/dhcpd6.conf snippet (values are examples - tx is time, mx is MAC in type 1 DUID):
host FOO-6pool_foohost { host-identifier option dhcp6.client-id "00:01:00:01:t1:t2:t3:t4:m1:m2:m3:m4:m5:m6"; fixed-address6 2001:db8::123; }
Tested working:
host FOO-6pool_foohost { host-identifier option dhcp6.client-id 00:01:00:01:t1:t2:t3:t4:m1:m2:m3:m4:m5:m6; fixed-address6 2001:db8::123; }