What could cause sudden loss of upload speed

[#1]

Hi
So I have been on fibre unlimited for over 2 years on an 80/20 package. In the past my speeds have been approx 50/15 and I was perfectly happy with this until last week on 4th October at 15:55 when suddenly my upload speed went down to 7Mbps. I am pretty sure no one was in my house at the time this change occured. I contacted Plusnet via web chat last night and they confirmed I am on the 80/20 package so I dont know why my upload rate has decreased.(Question 135686927) So can anyone think of what could of happened to change my speed? To my mind it looks like something happpened in the fibre cab or the exchange what do you think? Here are the stats and events below and as you can see 4/10 my upload speed suddenly decreased.

I have tried rebooting my router a fritzbox but no affect still stuck at 7Mbps upload.

Any thoughts?

Thanks

[#2]

This is weird because the same thing happened to me a few years ago with BT Infinity. I had normal upload speed of around 14 mb for quite some time and then all of a sudden and still to this day its max 6 mb at a push. Bt tried loads of different stuff but found nothing and just said upload speed isnt important :S thats why i changed to Plusnet (yesterday) hoping the switch would help (wanted to change anyway) but sadly still this 6 mb cap thing, and as i do youtube videos and also want to live stream games but 6 mb is a struggle and more upload would be amazing!

[#3]

And here is a screen shot a year ago if this helps

[#4]

I notice that your SNR is down around 4 - 6 dB, which is hitting the bottom of what is usable. Maybe there is a new line fault, or some new source of crosstalk, and the equipment has dropped the speed automatically to do the best it can. Would that make sense?

[#5]

Hi Thanks for the reply. I havent added any new equipment and the error happened when no one was at home. If I draw a blank I will see about getting a new cable from the router to the master socket.  Also I will read up about SNR and VDSL as I know very little about this.

[#6]

I don't think it's anything your side of the modem that's the problem. It's the connection over the phone line from you to the green cabinet in the street that seems to be problematic. It's got noisier. When that happens, the equipment automatically drops the line speed.

(edit - added for clarification)

By "equipment" I meant the BT equipment in the street cabinet, not your equipment.