HomePods and smart plugs "Not on the same network"

Best greetings!

I just purchased and installed the Netgear Nighthawk RAX80 with triband 2.4G and 5G, replacing my old 2.4G Apple Airport Express. I turned SmartConnect on, and connected my devices.

The network sort of works. My computers work. But my HomePods keep telling me they "are not on the same network" as my iPhone. Wait a few minutes, and they work. And then off again. Also my smart plugs go on and offline in a similar way. My problems are specifically with my 2.4G smart plugs and my Apple HomePods. My iPad, iPhone, and computers work fine.

The Device Management screen of the Nighthawk app shows that all of my smart plugs are on the 2.4G band, and all of my Homepods are on a 5G band. That's correct, right?

I have followed instructions and done several resets of devices, network settings, and factory rests of all my devices. I have tried using my Nighthawk with SmartConnect on and with it off. No improvement yet.

I am fairly computer savvy but new to network troubleshooting. Is there a tool to manually allocate which devices get bandwidth or which devices operate on which bands (beyond what is possible on the Device Management screen) so that I can make my network stable? Or might the problem be something else?

Help would be appreciated.