For about a month I was synching at 4.8 - 5mbps. About 4 nights ago my synch dropped to 2.4mbps and it won't go any higher now. If I leave the connection on over night it will be 1.9 in the morning, if I reboot the router it will go back up to 2.4bps.
Overall the speeds seem much slower. Snr is 14, but will drop to 1 or 2 for a while!
Some suggest leaving your router on all the time - I used to.
If you have problems with losing sync, particularly due to SNR, I suggest that leaving your router powered overnight is simply exposing yourself unnecessarily to the risk of loss of synch and synching lower.
Obviously if you lose synch during the day there isn't much you can do about it but you can avoid it happening overnight.
I'm in a similar situation and I now power the router down overnight.
My understanding is that BT negotiate synch speed based on maintaining a given SNM, 6 or 12 db or whatever.
It could be that if you typically have a SNM of around 12 db or slightly higher then BT may have adjusted the SNM they apply to you from presumably 6 db to 12 db, as in my case, based on recent history of disconnections etc.
It could be BT have done this as a very easy, if not very satisfactory way, of eliminating some problems.
I think 6 db equates to a speed change of about 2000.