The default rule has changed from all-IPv4 to all-IP. All-IP includes all IPv4 and all IPv6 traffic. The default rule for TCP traffic, either IPv4 or IPv6, attempts auto-discovery with correct addressing as the WAN visibility mode. A fixed-target rule with an IPv6 target appliance address requires the source and destination address type to be an IPv6 address. You must change the use of all-IP to all-IPv6. If you do not change to all-IPv6, use specific source and/or destination addresses.