On all new 20CN and 21CN lines, BT enforce a 10 day training period. This also applies to certain migrations.
During the 10 days, BT will monitor and adjust the line to suit the characteristics of the line to combat line noise or stability issues. This may involve altering the SNR (signal to noise ratio) or adjusting interleaving.
In this time, you may see the line drop for short periods of time whilst the line is being adjusted.
We suggest that you should leave your router plugged in and turned on for the 10 day period to prevent a lower MSR (maximum stable rate) from being set by BT. With newer 21CN installations, profile changes react far quicker than their 20CN counterparts, often in near-realtime.
Also, during the first 10 days, we cannot raise any speed related queries due to the tests that BT conduct on the line. If after 10 days, you feel there are still issues with your line, please raise a ticket via your control panel.