Sync speed dropped on fibre broadband

[#1]

I've been with Plusnet since February this year and this is the first time I've had a problem (except for a couple of times with dodgy gateways where logging in and out to get a different gateway fixed it).
From the first time my connection went live until recently the sync speed reported at https://portal.plus.net/my.html?action=data_transfer_speed was 77.4Mb. Sometime between 20th and 29th September this has dropped to 67.4Mb. My set up has not changed at all, no new router, no new phones, no new lines and no work by BT on my street that I've been aware of.
I keep track of my speed fairly regularly using www.speedtest.net and I can see from this that my download speed dropped to match the drop in sync speed sometime during the dates I mentioned. Up to and including 20th September my download speed was reported between 71Mb to 73Mb, unfortunately I did not do another test until 29th September so I only know something has happened in those 9 days. Now my download speeds are between 61Mb and 63Mb. My upload speed has also shown a small drop from around 17.9 to 17.5. Latency has also risen from around 10-12ms to 19-21ms.
I've tried running the fault checker at http://www.speedtest.btwholesale.com/ but this does not show any issue. I've also tried 2 different routers and switched off and on all the equipment several times over the last few days but nothing has changed.
Is there anything else I could try to get my sync speed back to what it was?
Many thanks

[#2]

This is very similar to what has happened to me, although I stopped checking some time ago, but my profile has dropped from about 72 to 56.  Probably just coincidence (I have been advised that it's likely to be down to increased fibre take-up in my area), but it's interesting that it has happened to us both at the end of September. 
There is of course a possibility that we have both had an influx of new customers in our areas.  Do you have a University in your town?  We have two.

[#3]

No I live in Aylesbury, no university and quite a quiet back street, no new builds nearby or anything like that. Support did a check on my line but said there was no fault or cross talk detected. It just seems strange that my sync should drop for no apparent reason when it was running for 8 months with no problem.

[#4]

Hi dhrae,
It is a chance that this is the same cause as lorisarvendu decrease in speed as discussed here.
Again your estimated speed is showing line speeds is currently similar to what you're getting.

We've got your latest response on your ticket and we'll see if there is anything that we can find that has caused this.

[#5]

I've attached a screenshot of my speed test history from www.speedtest.net, it may give you more insight, at least it gives an indication of when things changed.

[#6]

There's no indication at the minute why it has dropped, we need to wait for our faults team to pick this up to see if we can spot anything.

[#7]

Well I've raised a ticket for mine.  Let's see if there's any commonality.