From the exact 40Mbps downstream, allowing for the couple of kbps that VDSL2 syncs always seem to lose, I would say it is a simple case of banding.
Depending on what the fault was and how long it lasted, so the error rates that caused the banding, DLM will remove it perhaps in steps over the next few weeks to months, assuming the error rates are now acceptable to it.
Plusnet can see the banding on their diagnostics if they look, but if the line is now clean there is little to be done. It needed the engineer who cleared the fault to request a DLM reset at the time.
I would suggest the poster stops doing any deliberate disconnections.
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