I am currently looking after my parents who have a BT HomeHub 6. When looking at the connected devices I see all my devices are connected to the 2.4GHz band despite many of them being capable of using 5GHz.
Using the Wifi analyzer that comes with my laptop appears to show that although the 5GHz is enabled on the router, it is not transmitting. I can see a neighbours 5GHz band and if I turn on my phone's wifi hotspot, it too is visible.
I've tried going in to the wifi settings and splitting the SSID's but no joy.