Any Update to this? I just connected my gx20 router to my Spectrum Cable modem last night. I'm able to get everything working through the router and the Meraki-Go app is seeing the devices and types of traffic. My problem is slightly different from the original poster. When I go to the app, under Hardware, it shows that my device is alerting (although the LED is white) and when I go into the device, it shows "Has never connected to the Meraki cloud". It doesn't show an IP address for the device either.
Any ideas? I have not rebooted the spectrum cable modem.