I upgraded to BT Full Fibre 100 and have FTTH. In the days after upgrading, my speed was a rock solid 140mbps on speed tests both via BT and external and there were no issues. However, since then, my speed has dropped to under 100mbps even when connected via ethernet and with no other active devices. I am wondering if my profile has gotten stuck somehow?
your profile is not stuck on FTTP so have you tried checking connections and then do factory reset of the hub by pressing recessed button on back and holding 20/30 secs until hab lights flash then run btspeedtester or fast.com
Its the same speed on my old SmartHub 2 (that needs to be sent back) and the replacement too, so doesn't sound like a router issue? As I said, on my old SH2, it was 140mbps without any issues after the upgrade. Its gone down since.
Can you run btspeedter with ethernet connection and post results. You can also try fast.com