DynamicDNS configuration does not sync to HA secondary
If DynamicDNS is configured on the HA primary firewall, it's configuration will not be duplicated to the secondary. I suspect this is because it can only monitor an interface IP or gateway group, and not a CARP VIP, thus having this in an HA config could be a "bad thing".
There needs to be some option there to watch for the CARP VIP status, and remain dormant until the status is Active. Oddly, this seems to be the behavior when it is configured to watch a gateway group (assuming the gateway group is configured to use the CARP VIP) in a multi-wan HA situation - but that may need to be verified too.