Plusnet is a mess (packet loss)

I have 40mb fibre broadband from Plusnet which for well over a year and a half was absolutely fine. Around the start of July I was promised a free upgrade to 55mb which didn't materialise. Instead, the connection began experiencing large amounts of packet loss during daytime and evening, but virtually none between midnight and 7AM.

Despite a very long and active thread on their forums detailing the same issue among a large number of people, when I submitted a fault report they appeared oblivious to any underlying problem and I didn't get anywhere. After several weeks exhausting their very support (which takes up to a week to respond and isn't helpful when it does), I disconnected for a few hours before reconnecting and ended up on a different part of the network, and all was fine again.

Until yesterday...

I noticed that the 55mb upgrade had been switched on at some point, but the reason I noticed this was because I did a speed test when trying to diagnose an unreliable connection. Yes, the packet loss is back.

So I disconnected again hoping to end up on a different part of the network, and it sort of worked in that I went from 200.* (or was it 209?) to 146.198.*, but unfortunately 146.198.* is getting around 20% packet loss.

Oh, and since reconnecting, I'm back on 40mb.