I agree that it sounds like a HR fault - the upstream SNRm is displaying typical behaviour for either HR fault or faulty filter.
Your symptoms sound remarkably similar to the fault I had which ironically started the day after I'd started migration from adsl2+ (Be) to fttc (Plusnet). Because I'd just started the migration process there was little I could do, and I was half hoping it would clear when fttc got connected.
I didnt have QLN & Hlog from my adsl2+ line, but from what I can recall the SNRm behaviour looked very similar
Symptoms were all the same as you mentioned except this one
Occasionally, the upstream SNRM can start a period of erratic drops. No obvious trigger nor end; can trigger a resync. I found that people phoning me could trigger this off - I only realised later when I'd tie up a message time on the ansa phone, but its possible that someone like my parents could have rung, as they seldom if ever leave a message. I'd also find that for no reason, the upstream SNRm would sometimes start to slide, sometimes I could bring the upstream SNRm back up by dialling out and then replacing the receiver.
Once fttc was installed things werent much better, so BT duly called out. First was no fault found because my SNRm was so high (16db) so that it was sufficient to mostly stop the line dropping when the phone range. Because the line mostly stayed in sync then it was considered acceptable. I persisted with the fault because the upstream SNRm was mostly swinging between 1dB and 16dB and now only occasionally dropping the line.
To cut a long story short 2nd engineer found a corroded terminal in my BT66, this cleared a small v notch in my hlog & SNRm stopped the wild fluctuations, but I still continued to get the loss of about 12db on the upstream every time the phone was in use, but BT found this acceptable because the line would only drop a couple of times a week. Eventually it got a lot worse and voice started to be affected too. Then an engineer found a faulty NTE which corrected things for a while... It was only when voice degraded to unacceptable level that they gave me a new d-side.
Sorry this is shorter than it could be, I have graphs somewhere, but Ive been up since 5.30 to take dad to hospital. Im awaiting a call before I have to shoot back out. But the whole tale and graphs are in a thread somewhere
here