>> Last night he said his pings were pretty high. He went and reset the router and the rest of the night was fine.
Line conditions could have changed, resyncing the line could have caused slightly lower sync speed but increased the SNRM.. therefore fewer errors and packet loss.
Without the stats we are blind though and just guessing what is going on.
The following is pure speculation, but it would certainly fit the symptoms described.... that the line could be experiencing noise issues in the evening which starts a chain reation:-
The noise reduces the SNRM, which causes errors, which causes packet loss, which causes noticeably increased latency.
The 21CN DLM doesnt react as soon as the Openreach DLM for FTTC and is a bit more lenient with the error rate before it starts profiling a line.
[Moderator edited: Typo fix.]