You cannot manually move to another band if smart connect is enabled.

Is enable authentication always checked? or it will uncheck automatically in a while? I never heard of this kind of issue. What's the hardware and firmware version of your C9?

What's the model number of your router? Generally the ports are closed by default. And you can change the login password and disable remote management on the router for security concern

Try this: Modem >>> google wifi unit(router) >>>PA9020P..... PA9020Ps>>>google wifi units (APs)

I am quite interested in this case. Can you share the model number of your AV2000 powerline adapter? And if the google wifi units are all wired connect to the powerline adapter and the google wifi...

I happen to know it. The Frequency Range of TL-PA4015PKIT is 2MHz - 67.5MHz.