Yes, the update zeroed the counters. But then, everything's working well at the moment so I have no cause for concern. They're still at zero.
Sounds as if there's something "upstream" from TFP's friend's master socket that will need Openreach, ISP, or other techie input.
I have a spare decent quality modem/router (my old Draytek) that I take to friends' houses to check their systems. Sometimes it does a lot better than their ISP supplied job: a new one from the ISP fixes it most times. I doubt that would help in this case.