Gigablast is a joke!
First time I installed the router I had a similar situation as you. Had to contact customer support for them to fiddle with things on their end but...
They call it gigablast but they say their top speed is 940Mbps.
Before the quarantine, the top speed I would ever get would be around 700Mpbs and Cox would always give some BS response for that; always blaming connected devices. Even with my laptop wired directly to the modem and no other devices on the network, it was never more than 700.
Now during quarantine, it doesn't go beyond 300 Mbps yet I haven't seen my bill lowered for not giving me the speed I'm paying for!
They are blaming high demand; even reps saying so on the news and recommending not to download system updates "during peak hours" WHAT A JOKE!
Uh... why market blazing fast speed if your network isn't going to be able to handle it?
They've just gotten worse and worse.