Unfortunately, BT Smart Hub 2 is not able (at least for now) have different SSID (name) for 2.4 GHz and 5 GHz wifi networks.
At some devices, this means, as device will connect rather to 2.4 GHz instead 5 GHz network, where you might experience these slower speeds.
Try on SH2 in advanced setup switch off 2.4 GHz entirely and repeat your wifi test speed to see, if that helps.
Just be aware, as some legacy devices, and many WiFi lights/bulbs might not be able operate on 5 GHz Wifi, and if you switch 2.4 GHz down, you might lost them from network.
Also, many devices allows you to check, what’s your physical speed between phone (example) and router. On Android you should head into Settings -> Wifi and you shall see (i) on right of the network names. When you click on (i) of active (connected) WiFi network, you will see additional info. You are interested into “Link Speed”
For example, my 2.4 GHz network has “Link Speed” 192 Mbps, and give me 40-73 Mbps downlink only. Without going to technicalities, that’s approximately match what is expected.
My 5 GHz network has “Link Speed” 866 MHz, and giving me 400-510 Mbps download, what again matching expectations.
These numbers might be different at yours, that will be depending hardware you using (e.g. what is capable WiFi card at device itself, and limitations of SH2 itself as well). But might give you idea, alongside of test with 2.4 GHz WiFi off experience, where might be problem.
Not sure, if iOS allowing to show physical speed of WiFi.
Also, my UTP (cable) connection giving me 900+ Mbps downlink, but that will be heavily dependent on HW you using. Cables has categories, you looking for CAT 5E or CAT 6, to get maximum from your FF900, but also need network card capable of speeds you aiming for.
