I have a Raspberry Pi monitoring my HG612 modem.
Nothing of note in the graphs. Connection normally very stable (connected for months at a time).
No change at all in my Sync speeds. It is just my Upload throughput that has dropped from around 6Mb to 1Mb about 48 hours ago.
I've never been happy with my downstream sync speed. I've had 3 open reach engineers over recent years. This is as fast I can get. Lots of crosstalk in my area. Over the years there have been a couple of occasions where the cabinet must have reset and kicked everyone off. My HG612 resyncs quite quickly at over 50Mb in these situations. As everyone else comes back on line my SNR drops like a stone until it resyncs back at around 42Mb.
I used to get a max attainable of 70Mb when I was on Digital Region all those years ago (but never synced more than 40+Mb as that was all they sold).
I've been on an online chat with a TalkTalk agent for over a hour now. Keeps asking about filters, master sockets etc etc despite my Sync speed being fine.
OK, good to know you already have line stat's monitoring capabilities with the Huawei HG-612 modem & RPi combination.
Can you possibly post some DSLStats snapshots, specifically:
HLog, QLN, SNRM, Bitloading and "Average Error Rates by Day" graphs.
Ensure DSLStats tone range is adjusted to cover all your active range before snapshot is captured.
I've asked about DLM / Profile resets and he says he can't do them - has to be done by Openreach (true?)
Yes, but have to be requested by the ISP.
Plusnet certainly used to get this done quite quickly via an OR request, not sure what TT's current policy is on DLM resets.
Have you tried the BTw Availability Checker by phone number, link supplied earlier, this will indicate what speeds your line should be capable of and what your handback DS speed threshold is.
Crosstalk is always going to be an issue on VDSL-2 FTTC service in the absence of vectoring which will never happen now, if you are unlucky and your line happens to inhabit a heavily populated DSLAM cabinet in a high density area there's not a lot you can do other than pray for FTTP service being available sooner rather than later.
First line ISP telephone help is as you have related very basic with the operatives just reading from a script with very basic understanding of what they are talking about, I have read that some parties have had good service from TT's second line technical service if you can manage to get your issue escalated.