The 2018-12-30 stats have an unusually high INP level of 4.0, so that's probably on a banded profile, even if it's not at the top of the band. The banded profiles go with higher downstream INP levels than usual, I think there are even two different levels that can be selected for some of the banded profiles.
From the BT diagnostic dumps on the portal ...
18th December, using A&A's chosen settings ..
Product Info WBC End User ACCESS
Profile Info WBC 3M - 6M Medium delay (INP 2) 6dB Downstream, UC Medium delay (INP 2) 6dB Upstream (ADSL2+)
BRAS Profile adsl350024th December after A&A reset to default ..
Product Info WBC End User ACCESS
Profile Info WBC 160K - 24M Medium delay (INP 1) 6dB Downstream, UC Medium delay (INP 2) 6dB Upstream (ADSL2+)
BRAS Profile adsl3500
Today 15 Jan, this is the dog slow but zero errors configuration it's settled on ..
Product Info WBC End User ACCESS
Profile Info WBC 2M - 4M Medium delay (INP 4) 6dB Downstream, UC Medium delay (INP 2) 6dB Upstream (ADSL2+)
BRAS Profile adsl3500Currently back and forward between different parts of Openreach as usual. Can't raise a Broadband fault as there's noise on the line, PSTN fault cleared because engineer thinks noise is not too bad, back to a BB fault, cleared again as all tests are OK, back again as a Lift and Shift - engineer's gone to the exchange tested and apparently decided it's not needed.
While BT's been continuously saying there's no fault anywhere, the line dropped three time today with the same symptoms - A&A receive report that line has dropped, PPP fails, however line actually stays in sync and PPP stays down until a DSL retrain is triggered in some way.