dont know if you guys recall but I have always had loads of upstream FECs on my line and its never caused an issue with DLM.
as for things happening around 9pm mark and carrying on for a bit before trailing off - seems an odd time for any kind of automated system to be triggered. Could be a bug I suppose, but bugs are not well known for being regular as clockwork every 24h (unless human error during setup is in the mix). From working at the other end of the pipes, that time period screams out to me "the time when the most streaming, browsing and porn watching is being done". food for thought.