I bow to the more experienced members but due to the early morning resyncs it does seem something happened to the line, DLM intervened and enabled Interleaving causing drop in sync speed and increased ping and then decided the line didn't need any interleaving just a slightly reduced sync to keep errors under control.
Gut feeling new cross talker impacted your line, DLM has intervened sorted it out and you have lost a very small amount of speed. Given new cross talkers can drop your speed by 10-20Mb it could have been much (MUCH) worse.
The trick will be is the line stable enough if not interleave may be reapplied if you manage a few days without intervention hopefully you are sorted until another cross talker appears
In the absence of detailed line stats, I concur with your gut instinct, but I have a little bit more to add.
If the DLM intervened at 1:30 am on Monday, then "Something" happened on Sunday causing DLM to add Interleave and Error Correction.
The Error correction overheads will have caused the loss decrease in sync and throughput speed.
The fact that DLM put it right again within a couple days suggests that
1) It must have been on profile INP=3
2) It was a 1st offence and hopefully a one off caused by a single burst of errors.
I doubt DLM has anything more to give back - if it had gone to INP=4.5 the other day, then it would have taken longer for the latency to return to normal.
Back to the topic of crosstalk - DSM (dynamic spectral management) makes it less likely that sync speeds remain the same during periods of sync.
Power goes up and down depending upon crosstalk situation meaning more variable sync speeds. I mentioned about a week ago about the possibility of power wars between you and a neighbouring cross-talker depending on who sync'd first - more so now than previously.
Mine is doing some weird things right now as I see DSM stepping down my power.
To add insult to injury I've also been interleaved after a single spike of CRCs/ErrSecs lasting for one minute and DLM still hasn't forgiven despite it now being over a week. Mine isn't first offence though so it's taking longer :/