I was hopeing for a better insight into a possible cause because in my case it coincided with downtime...
Attenuation looks OK, lower than mine which is about 38dB for D2 - I'd guess about a 400m loop length.
What's killing you compared to me is high noise. You have fairly high broad-spectrum noise, about 8-10dB higher under about bin 500 which is probably ADSL2+ crosstalk and then falls off to about -120dBm/Hz across the board. I don't know for sure but this is probably mainly VDSL crosstalk. I don't think any band predominates apart from the ADSL2+ frequencies so it's probably not an external source of interference.
Your current SNRM is 6.3dB so your target SNRM is likely to be 6dB. Therefore you're not paying any "DLM penalty" for previous instability.
How you map that to exactly why your sync has gone down I don't know. If your attenuation had gone up perhaps one would look to disturbed joints but it looks quite good at the moment. As the main problem is noise which looks fairly broad-spectrum it could be the issue is increased cross-talk.
I know it's normal for attainable to be higher than sync, I asked if it was normal for the gap to be so large. As of this morning though the gap has narrowed.
It bounces around a bit. The higher the SNRM the wider the gap between current and attainable but squishing figures from over 1600 bins into a single SNRM makes the relationship difficult to follow.
Originally my "attainable" was 41-42Mbps for a sync of 39999Kbps. Then my modem died and in doing so convinced the DLM to set a 9dB SNRM target. At that point the attainable was about 40.2, sync around 35Mbps and SNRM around 9dB. Then the modem was changed and briefly sync went to 37 with a 6dB margin and, again an attainable of 40.2-40.7Mbps.
Then something odd happened overnight and the DLM went to a 12dB margin, sync crashed to 20's - I was so peeved at that I didn't really look at the attainable!
Following a DLM reset it went to attainable 40Mpbs, sync 35Mbps, SNRM 6dB, then slipped to attainable 38Mbps sync 33 (grrr!) last weekend still at a SNRM of 6dB. Currently sitting at attainable 37 (lowest it's been) but sync just over 36 (go figure) SNRM still 6.
So for a SNRM of 6dB (or thereabouts) I've had a gap between attainable of anything from 1-5Mbps. I suspect if I had all the graphs from all the points in the tale I'd be able to figure it out but lacking that it just looks a bit random. In the figures you gave it was about 6Mbps at 6.3dB SNRM which is similar to how mine was at one point.
Unfortunately I suspect we're both suffering from increased FTTC take-up. I'd be really interested to know how many people now have FTTC on my cab and on the link to whichever DP I'm on. ADSL speeds here were rubbish previously owing to long (~5Km) lines so I had expected a healthy uptake. Sadly I doubt there's any way of finding out.