Thank you for posting the question.
Based on your information, I think the following instances could have caused the issue:
A. the Micro USB Host OTG y-Cable/ Micro USB Power
B. the new MAC address of the adapter is not recognized or filtered by the network router. Or no valid IP address is assigned to the adapter.
C. the USB2-E1000 adapter
D. the device driver in the Nvidia Shield
If it’s possible, please try another simple OTG cable that does not has power functionality. A micro USB (USB 2.0 specifications) is not designed to do data transfer and power charging at the same time. I am not sure what the y-cable is doing. It is possible that there might be some signal interference or something.
Next, please make sure that your router is configured to accept the new physical address of the USB2-E1000. As far as I know, Nvidia Sheild and Android in it would not allow you to set a static IP address. It is required that the network provides a valid unique IP address to the adapter dynamically.
In order to verify the USB2-E1000 adapter works correctly or not, if you have any Windows or Mac PC, please try to use the adapter with it. (Sorry but you may need to install the device driver of this adapter to the system though. If it’s Widows, Windows Update would do it automatically for you.) If it didn’t work, please contact us so that we could assist you.
If there was something wrong happened with the device driver in the Nvidia Shield, unfortunately there was not any way for users to fix that since Android doesn’t allow users to install/re-install any device driver. If you have not done so, please apply the latest Android update to your Shield.
Hope the above helps! If you needed any further assistance, please directly contact us at firstname.lastname@example.org