How to Fix Port Forwarding in Asus RT Routers

It seems that there is a problem with the firewall in ASUS routers in stock firmware and even in Merlin ASUS Firmware.
After a few hours the port forward is no longer working, you need to restart your router every time to make it work for another short period of time.

So in order to make it work you need to disable the Router Firewall, not a very good solution, but we have not found yet a better option.