Tixati shows that the IPv6 port is blocked on the DHT Node Table tab.  It is not blocked on the public IPv6 address, but it is blocked on the temporary/privacy IPv6 addresses.  I'm assuming Tixati is not specifying a source address preference.  Per RFC 6724, the default is to prefer temporary addresses.

There should be an option to prefer the public IPv6 address (which is ideally on by default). See IPV6_PREFER_SRC_PUBLIC in RFC 5014.