If you mean along northern end of Tanfield Road, I am not surprised.
BT line checker only shows FTTP available in a few roads (Bewdley Grove, Milton Road Cicle, Swanwick lane are a few I have checked and are available).
So although BT/OR installed the fibre that should have covered most of old Boughton, it seems they have only enabled some of the addresses. Most likely the cabs on the wrong side of the stream are not enabled for old and new houses alike.
I suspect that the FTTP on the west side of the stream is fed from Monkston, and east of the stream is united in waiting for the feed from Newport road (that has been possibly ongoing for a while).