If you are close to the exchange, but not too close, this may be the effect of customers on cabinets futher out moving to FTTC and thereby reducing crosstalk on your pair as they are no longer using data in that cable. This only happens when a cabinet further out is enabled ( or provided) that was using the same cable as you.
I beleive that this would only happen when a new cabinet is provided as normally the Cables to a cabinet are different to those serving EO customers. However the EO cable would be intercepted to put the new cabinet in place for a cluster of houses some way from the exchange ( usually 100+) removing their data path from the cable serving you.
Edited by kitcat (Wed 09-Dec-15 20:37:53)