In November 2019 I received a Sagemcom 5364 TalkTalk router after signing up for a new contract.
Using the TalkTalk speed check initially my windows 10 laptop (with a 2.4 Ghz internal wifi) clocked 28.6 MB/s download speed. However a week ago the wifi download speed was only 5.4MB/s. Although wifi upload speed is higher at 9.4MB/s.
Rebooting PC and Router do not help - download speed on wifi will not go above 5.4MB/s.
However, if I plug in the old HG633 router I get between 20MB/s and 25MB/s on wifi.
I have tried two different external USB wifi dongles with 2.4GHz and 5Ghz and the windows 10 laptop will not go above 5.4MB/s download with the Sagemcom.
According to the admin pages on each router, the phone line is rate is around 39MB/s with the Sagemcom and 37MB/s with the HG633. If I do a speed check over wired ethernet then I get around 35MB/s and so I conclude that there isn't a problem on the external line.
With my mobile phone (in the same location as the PC) I think I got a 35MB/s download wifi connection on 5GHz with the Sagemcom. I also have an ancient laptop (ex Vista) now running Linux and this is connecting happily with around 25MB/s download speed from either the HG633 or the Sagemcom on 2.4 GHz.
The problem is not affected by distance to the router.
I welcome any ideas of what might be restricting the windows 10 laptop's wifi download speed to only 5.4MB/s with the Sagemcom.