Why is my Cox Gigabit Service CRAWLING???

Looks like my previous post went into the bitbucket. My configuration is much like yours, only an MB8600 on the front. Testing directly from laptop to the back of the modem, or via the primary Google router (using either Google Home or Google WiFi apps) typically show about 550 - 580. I'm on the 500 mbps plan. My signal goes from the primary router to a gigabit switch and I use an ethernet connection to each of the 4 remaining Google routers. If you have the Google WiFi app, you can run the full set of internet/mesh/wifi tests in series. More importantly, when the 'Test Mesh' function completes, hit the ellipsis in the top right corner to see details. That will tell you exactly how fast your secondaries are talking to the primary. Mine are routinely in the 500 mbps range. The Lenovo desktop I am writing this on is using wifi and hits 400 mbps +. My wife's laptop is on ethernet and will run about 500 mbps. Two things come to mind. With multiple nodes, you can have extra challenges with a device grabbing a connection and staying on it even if the device moves. My wife's Samsung tablet is notorious for that. She'll start it in her bedroom, it will connect on a 5ghz, and then bring it down in the basement where the 5ghz connection is weak, but it won't readily reconnect. She has to turn wifi off and back on to get it to transfer to a more appropriate node. The other question is which way are your Google nodes connected? If they are not using ethernet backhaul, is there any possibility one or more have a bad connection, and/or they are functionin in a "daisy-chain" fashion rather than "hub and spoke"? The Google WiFi app will give you good insight. If you can't run in, then I'd take a laptop or other reasonably portable device with an ethernet connection and test it hardwired 1) To the Arris SB8200 2) To the Primary Google 3/4/5/6 ) To each remaining Google router. OH, and are you using first gen or second gen Google routers? I should have asked right up front. Second Gen don't support ethernet backhaul. That makes network configuration more tricky, but the approach outlined above should help you sort it out. If you post back with more detail, I can offer more suggestions. If you are on Gen 2, you may want to put all of the routers in line of sight and check performance and ensure baseline performance is appropriate. After that, work on physical layout in the house, which may require using WiFi Analyzer or WiFiman or something of that sort to ensure each secondary router establishes a proper mesh connections.