Some users may get the Gigablast speeds they pay for. The problem is that Cox shares bandwidth among a population group (neighborhood). Following quote from their Internet Service Disclosure:
Our Internet technology is based on the Data Over Cable System Interface Specification (DOCSIS). DOCSIS is a shared access technology where a population of users shares the available bandwidth. This allows cable operators to take advantage of statistical multiplexing, a bandwidth sharing technique which is used to distribute bandwidth across the user population while providing a level of service designed to meet the needs of customers running the applications of their choice.
The disclosure what written on October 15th, 2016 prior to when Net Neutrality was repealed. Net Neutrality was repealed in the United States in June of 2018. So the speed statistics they provide in 2016 are essentially bogus since June of 2018. Internet providers in the United States can now throttle traffic (shape it) if it benefit the company.
This leads back to the "bandwidth sharing technique" they use across the user population (your neighborhood). You are sharing bandwidth among the other customers in your area.. The Cox nodes, equipment, etc in your area can only handle a certain amount of bandwidth.
A direct connection from a computer to your modem bypassing your router can give me you better speed reading. Also your modem signal reading's could be bad.