Battlefield 4 UDP Port 3659

You might have been behind 2 layers of UPnP enabled devices. That means the dynamic port forwarding would have been applied on the closer router (closest to host). The farther router (closer to internet) would not know how to return traffic since those dynamic mappings are not populated.

When you put a UPnP enabled device behind another UPnP enabled device, things have a chance of getting messy that's why it's not a recommended configuration when you plan on using dynamic port forwarding.
Is there a reason why you want to run a router behind another (unless you want different networks...but in a home environment that's a little silly unless you're labbing or want to segregate networks. In that case there are better ways then 2 routers behind each other.)

If you want to do that configuration, disable UPnP on the router closest to the internet. Enable UPnP on the second router closest to the host. Now be aware that if you plug in hosts on the first router then you won't have the ability to use UPnP.

If you just want more port density plug a switch into your primary router (with UPnP enabled) and plug your host into the switch.