Information
This checkbox ensures that systems on the WAN are never added to the SYN Blacklist. This option is recommended as leaving it unchecked may interrupt traffic to and from the firewall's WAN ports.
Solution
Navigate to Firewall Settings->Flood Protection->Layer 2 SYN/RST/FIN Flood Protection - MAC Blacklisting and set 'Enable SYN/RST/FIN flood blacklisting on all interfaces' to true and 'Never blacklist WAN machines' to true.