I think you have a bad cable. Should be virtually no difference between a 10 footer and the 50 footer unless you have a bad driver on the network interface card. Can you try another long cable? Can you try another port on the router? And is that a standard 100BaseT interface port on the XBox?
Thanks for your reply.
Not sure about the 100baseT. It’s just the standard RJ45 type connector on the back of the Xbox.