Swinging Max Attainable after Line "Fixed"

I had an HR fault for about a year. It finally culminated in one of the legs disconnecting, prompting OR to actual find and repair the fault. (Lost dial tone)

The engineer that responded seemed very thorough, and fixed the issue with the one leg, and also identified and fixed a fault on the other as well. He was down a couple of man holes to do this, and had to get another guy to help him who had kit to lift "heavy lids".

Now, the phone is working fine, but my previously solid 80Mb max attainable, now swings between 66Mb and 80Mb. A difference of 14Mb!

There doesn't appear to be any correlation with time or weather. DLM has me profiled at 66Mb, and the SNRM swings between 3db and 9db.

Any clue what could have happened. Is it worth reporting it to my ISP?

Nothing will happen if you report it

Noise is a variable feast and might just be cross talk from lines that are sometimes busy sometimes not.

What is likely to have changed, given that the line was simply repaired, to increase noise or crosstalk?

I had already taken a beating from crosstalk that reduced the max attainable significantly from install.

The more uptake of fibre on your cab the worse it can get but crosstalk is unpredictable. You might be affected but your neighbour may not. Equally did they repair the existing pair or simply switch you to another pair from the cab. It could be your old pair was unaffected but the new pair is (if that is what they did).

The "Impacted" values provided by the BT checker now give the worst case scenario, could always check your number to see what BT is quoting for "Clean High/Low" and "Impacted High/Low".

He said he repaired the existing legs.

I can't imagine that crosstalk can change that much (and back again) in 24 hours. The modems are usually left turned on.

Does the "swing" happen gradually over time, or just switch from 3dB to 9dB, and back later?

If it happens suddenly, it seems likely to be someone turning their modem on and off.

It's gradual, 9,8,7,6,5db etc. over a number of hours.

I can't find any correlation with time, weather etc. Nor can I imagine how any repair could have caused such a weird result.

it can be a number of reasons.

1 - they may have swapped the pair, and just told you they repaired it, for end user its usually same thing. The new pair may have dodgy sporadic crosstalk.
2 - the repair work may have somehow caused this new behaviour.

I think as voice is now working and BT will see 66mbit as a healthy sync speed you will have a tough time getting this resolved, unless it gets very unstable.