We didn’t publish all the information on your routing table, but from it we can see that you have a double NAT. So NoMachine has to go through two. That is, a router facing the internet for which you have a private LAN with IP address of 192.xxx.xx.x) and then another router for access to the private network/LAN for which you have an IP address of 192.xxx.x.x).
UPnP doesn’t easily support this type of scenario. In this particular case, our upcoming product NoMachine Anywhere would resolve this problem for you and the hassle of having to configure routers by hand or setting up awkward tunnels.
Until then, and if you have access to both your routers, port forwarding should be set up on the second one as you already did for the other that you mentioned.