This is what I was trying to mention before, for some reason the eero doesn't play nicely with the Airave at all for some reason and won't allow the device to pass the boot up.
You see the yellow Ethernet ports on the back of the Cable Modem right? Plug the Airave into any port instead and then power cycle the Airave again and or factory reset the thing with a little clip or something and allow it to do its thing, it should now connect.