Vdsl / snr drops permanently until after restart


On my TPlink Archer VR200v it happens at least once per week,
that the SNR drops from greater than 13dB to lower than 11dB (often to 5dB).
DSL Firmware Version:

When that happens only a
/etc/init.d/dsl_control restart
The SNR is back to over 13dB then immediately after the restart completes.

If i just wait, then it gets only worse until the restart happens automatically, in the middle of a movie. LOL

Why is that?

I mean: VDSL should recover automatically from temporary noise.
But: It looks like, on my box it does not, although the line is good.



Mmmh, in such cases it sometimes helps to look at the SNR margin for each individual sub-carrier.
One way to get started on this is found at https://github.com/moeller0/lantiq_dsl_parser, sure it is clunky and convoluted, but should allow you to get plots relayively quickly.
Like a good SNR plot:

and a bad SNR plot:

Notice the relative smooth drop in SNR over bins in the first plot, and the up and down roller-coaster in the second. In that case restarting the modem actually helped, because that lantiq modem of mine occasionally ended up in a bad situation where it could not get itself out of....