Just leaving this here for anyone just now dealing with this, was able to find this website with the answer. Basically you need to turn off "Energy Efficient Ethernet" for the NIC. Open up Device Manager, expand the Network Adapters section and open up the Properties for your NIC. In the Advanced tab, there should be an option to disable the Energy Efficient Ethernet option.
I just bought a Dell E7450 and having issues with Ethernet connection. When I connect Ethernet cable to laptop without docking station it works fine. But when it is connected through Docking station it does not recognize the connection. I have tried swapping the docking station and re-installing the driver without success.
Ethernet does not work when connected to docking station (E-port)