One thing that's not explicitly stated is you should aim to place your primary Wifi point as close as possible to the centre of your home. That's because the Google Wifi and Nest Wifi mesh system uses a fewest hops approach. If one of your secondary points can get even a weak connection to your primary Wifi point, it will do that instead of going through an intermediary Wifi point that may physically be closer. That's why not installing them in a straight line, and placing your primary Wifi point close to the centre of your home really helps, along with all the other guidance in that article above. If you still experience issues after that, you can consider extra Wifi points (though not more than 5) or look at hardwiring all your Wifi points.
