Don't bother with the chat support when facing complex issues. I have tried to use them as well and they explained to me that they have very limited access to what they can see about your modem. They can basically only see a red light/green light type of system related to the signal levels. They can't see event logs and probably wouldn't understand the event logs if they could see them. That means they can't identify intermittent issues with noise ingress, etc. They also don't always have very much knowledge about how cable modem infrastructure works; I had one of them tell me that upstream power levels are related to how many streaming devices I have connected on Wi-Fi, then the agent disconnected the chat when I pointed out that wasn't correct.
It's worth the time to call and wait on hold so you can speak to someone that has more knowledge and more access to your modem.