Thanks ...
and for the moment it looks like the problem is not due to my ASUS hub being faulty.
The entries for 'Data Rate' in the technical log wrongly use kbps when it should be Mbps. I remember that from when I last used the HH6 in 2017 but it is not surprising that it is still like that since the log also reports that the firmware was last updated on 15-Feb-2017.
I seem to recall that software updates happened automatically and overnight, but since my hub is so old do you know if it is likely to get a software update and if so then how long might it be for that to happen. I don't expect it would make any difference but the engineer might prefer if it was at the highest version.
The line fault was fixed by Open Reach engineer and now syncing at around 66Mpbs with actual download speeds around 60Mbps.
I've kept the BT HH6 powered on 24/7 but it seems to reset itself every 14 days or so. Is that normal ?
the 14 day reset is normal for some and does not affect others. unfortunately there is no solution apart from using a 3rd party router
from personal experience it the 14 day reset can just stop without any notice and you only notice when you check stats