Nighthawk R7000 continuously dropping internet connection after firmware update

It turns out I was totally misdirected by a couple of coincidences.

I had changed my firmware, so had considered that as the culprit.  At the same time, we're having building work done.  We checked that (cut out nearly all of the existing cabling), yet we were still having problems.  

What we eventually turned up was an incorrectly wired Master Socket.  The VDSL extension was taken pre-filtered, rather than from the filtered connectors.  That had worked perfectly happily for the last 2 years.  But it's likely the building work jogged something that just upset the balance.

Thanks for all your help on this.  But now I feel we've got everything working well enough again to brave the firmware upgrade again :)