Cannot Access Server from Home Network, but Cellular Works

[TheDreadPirate]

You do NOT need to set a known proxies address in your case. You can use your DuckDNS address on LAN but if you don't have NAT loopback the traffic will go out to the Internet and come back. With all the bandwidth and latency issues that entails. With NAT loopback the router will keep traffic local when the IP address of a domain name resolves to itself.