3.9.6.2 is actually now available on Draytek.com's website. If you don't want to wait, although they don't list BT as their firmware, you can try by the modem code (I believe BT firmware is MDM1, but you'd need to double-check)

Thanks edinburgh I have got a little further with the issue but still no resolution unfortunately. I went forward in firmware one step to 3.9.4_BT and that is where the problem begins, so it looks like its not the latest firmware after all meaning my issue begins with 3.9.4_BT firmware for whatever reason. I have flashed the 3.9.4_BT firmware .rst file and only entered my BT Broadband settings/Username and Password via the wizard while having only 1 windows 10 machine connected and the issue is present even in that basic setup. I then did the same with 3.9.6.1_BT .rst firmware file and tried other DNS servers also and the issue remains. Gone back to firmware 3.9.2_BT again and restored my config backup and all is well again. Not sure what to look at next.

Then you need to check your settings etc. I have 2762 and I'm running 3.9.6 MDM3 with no lag problems etc. Plus, there were no new features on the 3.9.6.

Why don't you post some screenshots, including your DSL status?

Line Statistics

Downstream Upstream
Actual Rate 79997 Kbps 19999 Kbps
Attainable Rate 81067 Kbps 29634 Kbps
Path Mode Fast Fast
Interleave Depth 1 1
Actual PSD 6. 6 dB 13. 9 dB
Near End Far End
Trellis ON ON
Bitswap ON ON
ReTx 0 1
SNR Margin 4 dB 12 dB
Attenuation 14 dB 16 dB
CRC 0 4097
FECS 0 s 0 s
ES 0 s 3172 s
SES 0 s 48 s
LOSS 0 s 0 s
UAS 30 s 3876 s
HEC Errors 0 0
RS Corrections 0 0
LOS Failure 0 0
LOF Failure 0 0
LPR Failure 0 0
NCD Failure 0 0
LCD Failure 0 0
NFEC 240 32
RFEC 0 16
LYSMB 5028 16

Really difficult to know without further details. Is it pages not loading? What message did you get?

Have you tested the new firmware by being connected via ethernet?

Have you tried other versions of the same firmware to test, and different modem codes? (WAN >> General Setup >> DSL Modem Code)

Have you checked MTU? Defence setup settings?

However, your upstream SNR is very high - 12db - and you're losing nearly 10Mbps somewhere. Is your wiring ok?

Pages load but slowly like a dial-up and not every time some pages/sites load as you would expect from an 80/20 connection none timeout and all load eventually, at first I thought it was a DNS issue which was why I tried other DNS servers to no avail. The Draytek is in a business environment multiple users and 98 percent of devices are connected wired through a switch. The 2762 we have is the model without wireless as we use Ubiquiti AP's for that. All testing is carried out with only the 2762 plugged directly into our VDSL faceplate master socket as it always is anyway and a single PC connected directly to the RJ45 port on the back of the router ruling out any other network equipment. There is no phone plugged into the phone line as we only use it for broadband our voice services are VOIP. I haven't tried other versions of the firmware yet i.e non BT ones. I have tried various different MTU settings 1492 is the suggested BT size and the path MTU discovery tool selects this when the detect button is pushed and starting from 1500. The stats I posted are from the router running 3.9.6.1_BT firmware but the stats from the router running 3.9.2_BT which works fine are virtually identical no big differences so surely if upstream SNR was the issue it would have the same effect on any firmware. Tried both modem codes available under (WAN >> General Setup >> DSL Modem Code). I have also reconnected the BT Business hub we were supplied when the line was installed several years ago and this works perfectly also ruling out a line/wiring issue. All tests/firmware changes between the working version and the latest version have been done without my router config so factory defaults and then my bt VDSL login details entered.