Some very interesting papers, les-70. Thank you for drawing attention to them :-)
DMT has a lot of graphing bugs or quirks, which make it difficult to know what we are looking at.
The plots overshoot past XMAX. The plotting code is buggy and doesn't adjust the interval when the first few DMTs are left for POTS. The Hlog is also plotted upside down to the norm. Attenuation is usually plotted on a negative Y axis, and runs vertically downwards from 0dB to -100dB. The SNR graph is also absent from DMT#32 to DMT#64 even though these tones are utilised in the downstream band.
Perhaps the biggest problem with the DMT graphs, which renders them useless for studying VDSL2 tonemaps, is the lack of detail to them. The graphs need to be vectorised using SVG or similar, and there should be zoom and scroll facilities.
What specifically looks like a bridge tap on your line? The papers you have linked illustrate the tap as a series of narrowband notches in the Hlog graph. These manifest at the fundamental frequency of the wave that is reflected back from the tap end, and at its harmonics.
However, your Hlog graph shows a single broad hump (actually a broad trough once the graph is correctly inverted).
To my untrained eye, the chief anomaly is the drop in bit depths between ~DMT#32 and ~DMT#56. This is probably due to crosstalk from other pairs carrying xDSL signals. There are also a couple of very focussed areas of noise at ~DMT#150 and ~DMT#280. This noise hasn't moved in any of the plot so perhaps it is due to RF noise or internal noise at the transceiver?
Interesting topic, thanks for posting
cheers, a