Two things show up in the stats.
The noise margin of 9dB, if it is the same on a reconnection, is I think the default setting for a C & W connection. The Office 45 default is 6dB, and the 3dB makes a difference of 700-1200kbps on ADSL2+.
Also it is possible the new BT DLM had lowered the Enta one to 3dB, giving another boost.
The second thing is that on 39dB attenuation I would have expected 11Mbps+ connection on the 6dB setting. That might just about have given you your previous 9Mbps throughput, but on the 3dB setting it would have been expected or bettered.
I wonder if you have a minor wiring problem. Have you ever checked
the ring wire, or the things in the Miscellaneous nasties on the menu there.
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