Internet speeds are half of what I am supposed to get

I currently have the Gigabit Plus internet plan where I am supposed to get download speeds of 1200 Mbps and upload of 200 Mbps. However, I connected my computer to the XB7 gateway modem via ethernet and I am only getting ~600 Mbps, sometimes less. This started to happen a 1-2 months ago.

I already contacted an agent online and did the recommended steps of renewing my IP and resetting my modem but to no avail. I have another computer that is experiencing the  same. I am using a CableMatters CAT6 ethernet cable.