I have a FG-60F and also upgraded from 6.2.3 ---> 6.4.0 ---> 6.4.2.
During the upgrade process, I had FortiDDNS service intact on FortiOS
6.2.3 & 6.4.0. When I upgraded to 6.4.2, FortiDDNS service broke. No
longer could see the Fortiguard DDNS server...
