It looks as though you still have a line fault, the reset would be DLM taking action to reduce your speed, not BT resetting your line.
I did not have a line fault when I noticed the slow broadband speeds a few weeks ago, however I got BT to retest my line and they say its perfect, with no problems.
I assume if I now want to pursue this with BT and raise a fault then I am going to have to put my BT Smart hub 2 back online so they can fully test and analyse my broadband issues.
I have just had confirmation back from TP Link support that all their DSL modem routers support VDSL2 technology, and don't support G.INP(G.988.4), see their reply below, might be useful in future queries?
As for my slow download speed, I have reported this to BT and will get a fault raised today as my speed is a lot lower than my BT minimum guaranteed speed, it was not a few months ago, so must be an issue somewhere.
TEXT FROM TP LINK SUPPORT EMAIL:-
Firstly, VDSL2 is the highest level of DSL modulation we have currently. So your device is running at its best manner.
As for G.INP (G.998.4), both of VDSL2 and G.INP(G.988.4) are methods to increase the speed, but they work on different technologies. Simply to say, VDSL2 is based on noise-cancelling technology to reduce interference during data transmission, while G.INP(G.988.4) increases speed by correcting errors of data transmission.
It's hard to tell which one is better, but all our DSL modem routers adopt VDSL2 technology, and don't support G.INP(G.988.4). I will forward this request to our R&D department, who will evaluate it.
I would like to thank everyone who provided me with information.
I had a BT engineer visit today and found although the line tested OK when I reported to to the fault helpdesk, it had loads of errors due to a bad cable. He swapped my line over to another cable and it has solved my download speed problems.
I am now getting no errors on the line and my download speed has increased from 26Mbps to 45Mbps. 🙂