Back end of Jan I moved to BT Infinity, and received the HH5. Doddle to setup, etc. A couple of weeks ago I got home to find the hub constantly rebooting. Unplugging the power didn't make a difference after it powered-up again.
After a call to BT, and performing a full reset, it stabilised.
A week later it happened again, and after going through the same trouble-shooting steps (this time a full reset didn't fix it), they decided to send me a new HH5.
After I'd ended the call to BT, I tried another full reset which seems to have worked again as not had a problem in the intervening days.
I now have a brand new, unopened HH5 sitting doing nothing as I wasn't going to replace it until things went pear-shaped again. By the sounds of it, I may not need to, if they're rolled an update out.