Yeah some routers are not super UPnP reliable. Some lose communication with LW for various reasons also. If LW has too many incomplete files for example attempting to connect when opening LW, then the communication with the router can become flooded & UPnP communication gets lost or never initiates.

My present router seems very good with UPnP. My previous one did not have UPnP so port forwarding was required for it.

I agree with Sleepless though, Port Forwarding is 'generally' more reliable because the port is always open regardless. It does not depend or wait on LW requesting the router to open a port.

Just one point, only one computer & program can use a particular port when port forwarded. Port forwarding is also based on ip address of particular computer or account user.