Slight improvement - I think

Now both sockets on the RJ45 work - left & right but only if one cable is plugged in. If both plugged in, the cable that was connected second can access the Internet, the first one can't.

Really confused. Clearly the socket is only taking data from one of the connections. What do I do to see both. Is there a crosstalk setting?
On the router there are 16 ports but the dual socket shows up as the same port number - if that makes sense. Basically, irrespective of which of the two ports I plug into, the same light comes on, on the router.