Haven’t we gone down this path before? 
And you said it is working.
So to clarify… you are connecting your UNO, with an Ethernet shield… to a laptop… using Internet sharing… and the laptop is connected via USB hub to a (most likely) cellular WISP? And it, surprisingly, is not working stable 
Since your UNO needs to be tethered to the laptop anyhow, just remove the Ethernet shield and use the USB link instead.