Remember a cross-talker is only added when a modem reaches sync and starts transmitting. It isn't necessarily when a connection is changed in the cabinet - self-install could just be when a subscriber gets home from work. And it doesn't have to be someone new - it could be someone returning from holiday. Or just getting up in the morning.
A modem reaching sync can have different impacts on other subscribers. It can cause an increase in noise, or an increase in errors, or both. Or nothing.
In this case, it isn't clear why DLM has made a change, but it might be because there was a resync the day before.
I'm approaching the XdB implementation with an open mind as to how DLM will have changed to cope, but I do expect to see some different behaviour. After all, the whole premise of using 3dB can make any line more susceptible to fast-developing changes in the environment ... so I expect DLM to have tricks up its sleeves for a faster response.
One open concern I have is this: How will DLM react if it has inadvertently made a line a little less stable - such that it causes resyncs rather than errors. I expect to see signs that DLM falls back by 1dB if it is "pressured" at all.
I can imagine a plausible method where DLM has had a hint that a line is less-than-perfectly-stable (ie after a resync), where it sets the "target SNRM" to XdB and a (new) "next target SNRM" to X+1dB in case there is a further resync.
With such behaviour, today's 5dB target might have been because there was a resync yesterday at 4dB and a further resync today.