Are you still in contract, if so BT should provide a new HH. I've always called to get mine, I'm very insistent they replace the unit and eventually they do (it is a pain though, they run checks and it usually takes 45 minutes approx start to end).
I only use 5Ghz in my household now, my iPhone only has 1 bar although it does not drop out. I do have a wireless AC 1200 Mbps booster as well, also linked over 5Ghz.
In my experience I've never got a firmware upgrade when I change settings in the HH, as already discussed. Not sure if that's a coincidence although other users report the same on BT forums. I really hope you get this resolved ASAP.
Worth noting, the replacements I've got are always recirculated devices and as such usually have relatively new firmware (in my experience). Not sure if they're all the same but my last one had the latest firmware already applied and had logs going back 6 months before I owned the device. I could see the firmware had been applied two months prior, as when I logged into 192.168.1.254 I could see last firmware upgrade and the date.
I had my old Type A replaced as it kept rebooting almost daily. New one doesn't exhibit this, so things do go wrong. Keep us informed!
Edited by ukhardy07 (Mon 11-Apr-16 13:39:53)