It doesn't look like DLM is causing these resyncs to me.
The strange pattern looks to be the "decay curve" on the SNRM graphs. From this, I'd suspect a fault on the line, or in the modem driving the line.
Looking back a longer period, I'd say there was a noticeable change around 10th October. Using the 90 day graph, you can see that was the end of a long period of uptime (which is otherwise not that stable), and a shift in the SNRM patterns, and a shift in the bit-swapping graph.
If you look at the graphs that show behaviour per tone (Quiet Line, SNR/tone and bits/tone), and specifically check the historic ones for the 10th and 11th October, you can see marked changes between tones 300 and 835 between those two dates. Notionally, the "after" graph looks like it gets less interference, but the "before" graph looks an awful lot smoother.
I can't say what those changes mean, though.