We are on Telecom Broadband. Our modem normally syncs at ADSL2/2+ line mode. Recently our speeds improved from normal: 8000 DL /1000 UL to around 12500 DL / 1050 UL. This lasted for one week.

However now the modem refuses to sync at ADSL2/2+ as the line type (as in will just keep retraining and will not even pick up the line stats such as DB, ATN, etc.), so I had to manually tell it to do G.DMT and doing that makes the modem sync up on its first try.

The speeds from G.DMT are similar to what we were getting - i.e., 8000/950. My question is why would our modem decide to gain the extra speed for a week, and now has stopped the extra speed and now wont connect as ADSL2? The day our modem got the speed boost, there was a chorus tech working in the street near our house.

I haven't checked / changed filters as it would seem a different problem that is external to the house.