Consoles frequently have issues with UPNP. They just sometimes don't like it...and it may be enabled by default on your router, which may knacker things up seemingly randomly. If you router is using it, turn it off. Then go into the console's network section and run the connection test. If it is unable to determine the NAT type, or it is reporting anything higher than a 2, then you may be running a strict NAT configuration that needs to be eased up. Settings will vary by router, but there should be some references to things like Secure NAT and such that you can try toggling. Consult your manual, or in the case of a managed router, contact your administrator.

There should be no need for any kind of port forwarding for this game. That is something to skirt around security protocols you may find at work or possibly a college campus, where they basically only allow things like generic browsing and media streaming by default. In such cases, then you may need to punch the holes. Just be warned that if you forward traffic to a specific device, you risk knocking things out of whack for other devices. When you let it be managed by NAT, you avoid that dilemma. Once your router makes an outbound connection to SE's server and notes the ports in play, NAT should track everything just fine. The exception is when the router is configured with higher levels of security in play that may cause issues. In the typical home network though, this should not be a problem.