The "Unable to load FortiGuard DDNS servers list" error is a common issue typically caused by DNS configuration conflicts, communication protocol mismatches, or firmware-specific bugs . It generally occurs when the FortiGate firewall cannot reach the FortiGuard servers to retrieve available domain options. 1. DNS Override Conflict
Check the FortiGate’s configured DNS servers: The "Unable to load FortiGuard DDNS servers list"
: An expired FortiCare contract can block access to these service lists. Verify your license status in the Upstream Filtering communication protocol mismatches