I'm new to TP-Link after having given up on most of the other consumer and SoHo router vendors (long story).
I just spent 2 days researching and debugging my 3 day old AX11000. I installed it with the standard options, but was only getting about half the speed my ISP delivers. I have Xfinity 1.2 Gbps Internet interfaced with a Netgear CM2000 Cable Modem. The modem has a 2.5 Gbps Ethernet port and is a great fit with the AX11000, however after instal I was only getting around 600 Mbps to my 1 Gbps Ethernet connected PCs.
I then spent an entire afternoon chatting with TP-Link support. After all that wasted time and running around, the problem was fixed with a very simple change.
The AX11000's Speedtest function is faulty. It reports speeds just over half the speed you're actually getting.
The problem arises in that by default the AX11000's faulty Speedtest results are used to set the router's QoS (Quality of Service) capacity limits!
Solution: On a web browser, go into "Advanced" -> "HomeCare" -> "QoS" and manually edit the "Total Bandwidth" to your actual Internet service values.
My AX11000's Speedtest was returning download values in the 600 Mbps range. My actual service is 1200 Mbps. As soon as I manually edited these values, Speedtest from my 1 Gbps Ethernet attached PC went from 600 Mbps to 950 Mbps, which is what I'd expect for a 1 Gbps attached Ethernet connection.
You can verify your actual ISP's (Internet Service Provider's) delivered speeds by connecting a PC via Ethernet directly to your Modem (you'll need to power cycle it to get it to recognize your devices MAC address) and running a Speedtest on your PC that way.
Note - if you have faster than 1 Gbps service, you'll need the appropriate adapter for your PC to archive it's rated speed. 2.5 Gbps and faster USB-C adapters are available for around $30 if you need one.
I found a lot of recommendations regarding turning Smart Connect off and other Wifi setting advice. None of that mattered. Remember the slow speeds were affecting Ethernet too. It was solely caused by bad QoS values being set by the AX11000's default setting to use it's own faulty Speedtest function to set capacity limits. I do wish there was a way in the interface to just turn QoS off! This is the first router I've seen that didn't have that option.
Note too that the AX11000's Speedtest function doesn't say what server it uses. On all my other device Speedtests I've used the same server and got consistent results.
Bill Finkelstein, retired high tech exec.