Cross feed - as in you are sharing the line with a neighbour? Would be readily apparent on the voice side, and unlikely, a source of external RF interference is more likely.
Interleaving and G.INP both retain the 6dB margin. Interleaving on FTTC easily drops the sync speed by 8-11Mps.
Kindness isn't going to cure the world of all its awfulness but it's a good place to begin. Daisy Ridley.
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Bridge tap means a length of wire running off in a third direction, an underground joint would not be a bridge tap.
Rejointing every line outside every property it passes sounds odd too. You probably have a joint outside yours, but only way to know is access to BT line records and even then some stuff is missing
The SFI engineers that have visited the property in regards to the disconnections suggest this is the case, they explicitly stated that there is no way to get the D-side cable renewed or that there is any spare capacity.