It’s recommended to upgrade to the latest firmware version.
Besides, you could try some following steps to help narrow down your issue.
======Below steps are to check if DDNS works correctly=======
1/ Go to ACEmanager webview (Eg: http://192.168.14.31:9191/admin/ACEmanagerX.html#)
2/ Make sure you configure the DDNS correctly. If possible, please capture the configuration of your DDNS.
3/ Configure Remote Access following the picture below
4/ Reboot the GX440 to make the change effective
5/ Access to ACEmanager through your FQDN that you configured in DDNS to make sure your DDNS works correctly
======Check if port forwarding works correctly======
1/ Go to ACEmanager --> Security Tab --> Port Forwarding
2/ Enable Port Forwarding and please capture your configuration of Port forwarding.
3/ Make sure Trusted IPs Inbound & outbound are empty
4/ You could try port forwarding WAN 80 to LAN 80 with host web server (Eg: the server connects to GX440 through ethernet port). You also need to check the settings of proxy in browser of your checking PC. If possible, you could use Wireshark to capture packets.
If the checking PC can connect to the web server, Port forwarding then works fine on your GX440.
5.If Port forwarding works fine with host web server on your GX440, then it will be ok for your PLC