Port Forwarding stops working on port 443 on FVS318G

Hello,

I have an issue whereby i have only to port forwarders enabled, Port 3389 and port 443. 

Port 3389 works perfectly fine no hassles. However port 443 keeps on closing or does not port forward. It works for about max 4 hours then stops port forwarding. 

Here is what i have tried:

Upgrade bios to latest 3.1.1-18

Disable the stealth mode

Remove and readd the port 443 forwarder

Hard reset the firewall

Enable and disable secure remote management with various ports

Tick and untick trasnlate to port number under inboude service rule

User different external IPS for the port forwarder

Tried setting the rule in DMZ WAN rules

Please help what else can i try

Thanks

Warren