From the Hlog plot, I can say that there is something abnormal about the metallic pathway.
I am hesitant at suggesting that it is the result of a bridging tap, as the shape is quite wrong. However, if I look critically at the plot, I can see very small undulations at frequencies lower than the minimum located at (about) sub-carrier number 3640.
For now, I think it would be helpful if we could have a description of how the circuit arrives at the premises -- an aerial or an underground feed, how the internal service feed reaches the NTP (network termination point) -- any joints/junction boxes, the type of NTP -- is it an NTE5 or a LJU and details of all wiring the end user's side of the NTP.