As an update, I tried setting my D-Link modem/router into bridge mode again, and this time it worked. So now Google Wifi is acting as the primary router with no double NAT issues. I believe my earlier problem may have been associated with the bridge mode I had chosen. I may have tried to bridge a combined Internet/VOIP, whereas this time on the D-Link I chose to just bridge “INTERNET” (as the settings call it). I stand by my position that the D-Link has the worst interface of all time.