No
Stop resyncing the line. Every time you resync DLM is likely to make the banding worse.
Why why why would you at a cap of 90Mb.
The cap is already 80Mb so setting 90Mb simply resyncs your line while doing NOTHING.
I don't think you should be setting a cap to trick your ISP in to sending an engineer. The engineer will simply plug his own device in (which doesn't have the cap you set) and you will get a £130 charge because your equipment is at fault.
If Plusnet won't request a remote DLM reset then you're stuck with it.
Your banding won't show on a GEA test till 16th February.
You have nobody but yourself to blame.
You continued to fiddle with your perfectly operating line simply because DLM enabled G.INP on the upstream.
I wish I had 74/20
I get 45/7 on a good sync.