I dont know about removal, but the 2 instances where I have been banded were caused by the same thing.

Basically these 2 steps

1 - line syncs higher than normal due to event like power cut.
2 - line has a period of instability that triggers DLM "whilst" its synced with the low margin.

The code in place seems designed to band a line if that happens instead of interleaving.

The first banding I kept for over a year, but it was removed when openreach did a full line reset, the second banding I still have in place now probably for about 5-6 months now I think. My current attinable is 20mbit over the banding, so that seems to have no affect on its removal.

Inadvertently low SNRM is a common affliction in VDSL2, whether sudden (as you describe) or gradual (slowly adding subscribers).

I now believe that DLM's first intervention step should be just a resync. No change to interleaving or retransmission. Certainly no banding. Just a resync.

funny enough banding got removed on my line a few days back, more info on my kitz post.

The problem with what you said is it doesnt prevent the line syncing too high again on the next power cut, whilst banding does. I think banding has been designed to avoid these type of situations.

I would be ok with just a resync, but I guess openreach are not, as it seems they dont like the idea of lines syncing above their normal rate because of power cuts.

I have to agree about banding used to avoid lines syncing too high. My line is banded as 14999 which after a power cut it will sync at that speed with a 4.8dB SNRM then after a few days it will resync at it's usual 12-14 Mbps.

Might as well post on this thread as it continues my improving sync speeds - there was a 5 minute power cut earlier this afternoon covering a wide area and when the power came back, the modem synced at 79999/20000! That has never happened before and is pretty good for 450m odd. It's holding up so far but the downstream SNR margin is only 0.8dB, so it's probably precarious. I haven't dared update the signature yet! IP profile is 74.1, 92.6%.

That sounds like you were one of the first to reconnect. But as you say, there is clearly no banding in operation.