OK fixed the AX1800 by disabling the 2.4Ghz bandwidth and just using the 5GHz bandwidth (both were enabled in the original router settings). Download speeds are now well in excess of 100 Mbps

I returned the MR3420 to the shop, and let myself be charmed into getting a TP-LINK Deco AX1800 (aka X20). Brought it home, set it up, ran the speed test: still only getting 60 Mbps of the 100 Mbps...

I just bought a MR3420 router and connected it to my 100 Mbps ethernet WAN, but the wifi speed is less than 50 Mbps even when I put my PC right next to the router. This is disappointing as the router...