As B*cat quite rightly says
SNRMargin and
SNR are not the same thing, they do have some type of correlation. I would not be surprised if the line has also lost a similar amount of true SNR.
Obviously I dont know for certain what caused this, but one thought is that the engineer could have been doing some sort of re-wiring that could have shifted a neighbouring pair within the same bundle. This could then introduce crosstalk on to gazaai's line. Note how things were better for a short while (possibly whilst the other line was disconnected. If he reconnected to a pair more adjacent to Gazaai's, it could possibly cause more crosstalk than the previous pair did.
I really do wish I knew what causes that jitter. All that I know is that on my line it can sometimes happen after remote sync if I come back up before my cross-talker, or Ive also seen it happen a couple of times after a crosstalker resync.
Although GaZaai says its now settled, but it does look like it has only done so after some remote action (resync) by one of his crosstalkers and he has lost even a bit more SNRm