Something similar on my side...
If I connect directly to the router the measurements improve, HOWEVER, whatever I download from normal sites is VERY slow..
I do not care much how fast it goes from home to Swisscom... The router shows amazing speeds... but in practice, anything I try to download from normal places is VERY VERY slow.. Even Microsoft or Linux updates download at less than 1Mbps..
I am really tempted to switch provider.