Okay. Looking at the specs of the Z390 Designare, all USB ports are Intel. I take it your GL850G is attached to an internal header which is USB2, not the USB3.1 one. Therefore that USB port is the root node and the one macOS interacts with. Sleep can be affected by polling or power draw. Polling is successfully defeated by the UsbConnector type, but as I'm guessing the GL850G is bus powered, perhaps (and I don't have one to test here) the chip itself has fluctuating power demands. If it does all it does on USB2 fuel, peaks and troughs are going to be more noticeable and have an effect.
As you say, I'm curious too ...