New Firmware on home hub 6a

Firmware version:
SG4B1000B522
Firmware updated:
15-Jan-2018

Speed increase due to the above being automatically installed by BT.

not yet

still have SG4B1000B316

I got it on Jan 12th. But my speed dropped.

Not me either, but I have an engineer coming round today to sort out the noise margin on my HH6.
Reading 14.6dB/14.1dB.

Seems to me to be about double what it used to be and I have problems surfing sites.
Sometimes takes an age to connect, even though my download speed is around 75 Mbps.

75 Mbps and 14dB noise margin - quite a lot of those around on short lines. At a guess your max attainable will be in the 90s.

My upstream syncs at max, with an SNR of 11 dB with max attainable well up in the high 20's.

Interesting, but I’m nearly half a mile from the cabinet, so not really a short run. Maximum attainable is an incredible 116386.

So, the sync speed is fine, speed tests fine, SNR is as expected and you have a very good low attenuation and low noise line. there is very little a BT/OR tech can do on site and when he sees those figures he may well do nothing. As for the problem you have, that may need addressing with your ISPs tech help desk.

Firmware version:
SG4B1000B522

Firmware updated:
11-Jan-2018

My Wi-Fi seems a bit flaky since the update, it used to be rock solid but now it seems to drop quite a bit.

My ISP is BT, that’s why they are sending an engineer.

And if that engineer is from Openreach they will look at the line stats on their kit, which should be similar to what you've shown and conclude VDSL2 is working as expected. Issue is down to ISP