I just purchased an Archer AX11000, and I was too surprised with slow connection speeds. 

I have a 600mbps plan, but I get 250mbps tops even after disabling QoS, antivirus and even firewall in the settings. I've also tried all possibilities with internet port connection speed, and swapped my cat 6b cables for cat8, tried to use the stock cable, and nothing happens.

I've tried it all. Latest firmware, previous firmwares, setting up QoS manually, disabling it...

Has anyone actually found a solution for this? I see no option but to return the router. I was getting the full 600mbps with my Asus RT-AC59U, so it's definitely something related to the new router. 

Oh, and please, do not send links to other threads (unless there's an actual hidden solution somewhere), I've checked all of them, too, as well as YouTube videos.

Thanks in advance for your help!