I plugged the tplink back in and its now working

previous sky stats
DSL Modulation Type:
Annex Type:
Upstream Downstream
Current Rate (kbps) 19999 79999
Max Rate (kbps) 30282 95843
SNR Margin (dB) 15.8 9.4
Line Attenuation (dB) 21.1 10
Errors (pkts) 33 0


current plusnet stats

Line Status:
Connected
DSL Up Time:
0 days 0 hours 4 minutes
DSL Modulation Type:
VDSL2
Annex Type:
Annex A/L/M
Upstream Downstream
Current Rate (kbps) 19999 60365
Max Rate (kbps) 26757 73273
SNR Margin (dB) 15.7 6.3
Line Attenuation (dB) 21.2 10
Errors (pkts) 0 564

Thats quite a hit you have taken on sync joining Plusnet!

It's almost always the case that an ISP switch will result in G.INP being removed, interleaving applied, and SNRM target returned to 6dB.

Unless you simply resynced at a noisy point in time this looks that more could be going on.

Given the current stats I estimate G.INP and 3dB would get you to around 77-83Mb.
Your line was previously capable of 95Mb.

The upstream also dropped 3Mb from the attainable which had no DLM changes so it could also be that a new crosstalker has joined around the same time.

It's "usually" 2 days for G.INP to return, and if very stable another week or so for the line to return to 3dB.

Just closing the loop.
All back to normal now with the real world speeds.

Line Status:
Connected
DSL Up Time:
10 days 13 hours 55 minutes
DSL Modulation Type:
VDSL2
Annex Type:
Annex A/L/M
Upstream Downstream
Current Rate (kbps) 19999 79999
Max Rate (kbps) 25349 81432
SNR Margin (dB) 15.3 3.1
Line Attenuation (dB) 21.2 10
Errors (pkts) 788 7790 <---------Incremented during the initial10 day resyncs. stable for 10 days now.

I pretty much get 74Mbps with single and multiple thread speed tests.