@robb35mm Yes. I tried a bunch of things, and I think what did it was to change the Wifi network adapter power settings in Device Manager. It was "MIMO Power Save Mode" under "Properties" - "Advanced...

I installed a new AC1200 as an access point. It is connected to another TP-link router via ethernet cable. When I connect to the AC1200 via wifi (Windows 10 PC or MacBook Pro), I get a speed of...