I've seen similar posts, but none with answers that seem to help, so will give this a try:
I have the XB6 gateway with the Gb Internet service. No VOIP service. I have a handful of devices that require ethernet connections, so bought a TP Link 5 port switch, plugged into one of the two LAN ports on the gateway. Second LAP port is connected to my NAS.
With the start of school, I needed to add a couple more wired devices, so upgraded to a Netgear 8 port switch (GS108) and connected the devices, and everything worked well for a couple days. Woke up one morning to find all my home automation hubs offline, and also found that my laptop had reverted back to wi-fi, and the ethernet connection had a "No Internet" message.
Did a number of resets on all devices, including the gateway, which seemed to fix it for a while, but then all wired connections on the switch dropped. Figured I must have had a bad switch, so ordered a replacement, and in the meantime, dropped back to my five port to get the automation hubs back online. Like with the eight port, connections came up fine for a while, but then dropped.
The new Netgear switch arrived and exhibited the same pattern of "works for a bit, then drops".
I have tried both of the LAN ports with the same behavior. I've also cycled through multiple CAT6 cables with no change. However, if I plug my laptop directly into the the lan ports on the gateway, I am able to access the internet just fine.
The Gateway is not in bridge mode.
Am I missing something re: configuration of the gateway to support an attached switch? I'm sure I don't have three bad switches, but something's causing all of the switch-connected devices to drop, and full resets of everything, starting with the gateway, then the switch, and finally each device, doesn't fix the problem.
It is possible the gateway is failing? I can run into the Xfinity store to swap it. And if I do, should I ask for the XB7 so I will have 4 LAN ports available directly on the gateway (I've read questionable reviews of the XB7).
I am glad to see your question as I have had the exact same issue over the last week. Unfortunately, I am equally lost and I can not provide an answer.
Everything was fine with a 24-port switch until last Friday. I went back to using a smaller 8-port switch yesterday and things are working with that, but I would prefer to use the 24-port switch I have so it will allow me to use more wired connections. Any assistance anyone has would be great!