When I first got BT Infinity and my HH5 I was annoyed that the router rebooted itself 1/2x a day. It stopped doing it about 9 months ago and I'd regularly get 6/7 days before a reboot. In the last 2 weeks it has started again and I'm getting beyond sick of it.
Nothing has changed at my end, the router firmare is still from June 2015, and I really CBA talking to a technician over the phone because they just drag it on and on and never actually resolve anything.
How do I get a new HH6 or can you recommend a third-party router to try and install?
A third party modem/router is the way to go. When I got Infinity the Hub 5 was dropping connection and occasionally rebooting in the few days I used it waiting for a replacement router, just like the Hub 3 when on ADSL. Asus, Billion and TP-Link all have good reports from forum users. Depends on exactly the features you need and the amount you have to spend. TP-Link start around the £30 to £40 mark and most people seem quite happy with their performance. Just remember to gar one for VDSL.