I recently had BT Full Fibre 100 installed and I was getting speeds up to 135Mbits over WiFi to my mobile. the router is a Smart Hub 2. I decided to upgrade to Full Fibre 300 . My WiFi devices connect at 800Mbps yet I only get around about 150Mbps over WiFi. A firestick that sits right next to the router only gets 110Mbps max when connected to 5Ghz. Even though the WiFi connected speed is also about 800Mbps.
I have a Meraki Appliance plugged into a LAN port connecting at 1Gb. When I speed test from this device I get 230Mbps and never more. No tried a laptop yet because no one in my household has ethernet on their laptops anymore arghh!!!
Testing directly from BT gets 306Mbps. The upload speed is always fine.
I've read there are issues with the Smart Hub that may get fixed with the next firmware roll out. Would swapping out the smart hub for an alternative device help? I have several Fritz boxes doing nothing and they are normally spot on or WAN/LAN speeds.