May I know which country are you in?
If you're in USA, it's recommended to upgrade to the latest firmware on the USA official website.
http://www.tp-link.com/us/download/Archer-D9.html#Firmware

Please be noted that your current configuration will be lost after the upgrade as it adopts a brand new user interface. And you will need to re-configure your router after that.

It's really rather interesting that the latest firmware is being recommended here but apparently only for US customer?.
If you trawl through this forum you'll find a number of dissatisfied UK based D9 customers who have invested a large sum of money in a router with a number of flaws in the firmware.
Flaws that are never addressed for what was TPlinks flagship DSL modem when I bought it. I got less than 6 months out of it before it was abandoned as a device receiving firmware updates. This has left it lacking a reliable and truly useable firmware.
There is one upgrade that keeps appearing and disappearing (030316?) on/off the website but again this is flawed apparently and no better in some areas to previous firmware and worse in others.
Whichever firmware you choose you'll be left a little dissatisfied as bugs get fixed and new ones appear. My recommendation is if it ain't broke don't fix it. If you upgrade to the latest firmware you could well find yourself in worse shape. The last UK firmware is now coming up for 2 years old.
I appreciate that hardware moves on and I certainly don't expect a product to last forever. I do however expect it to be adequately maintained. Sadly the D9 has not been.

Radar, I wrote a long detailed and somewhat scathing post on 17 March about the lack of support for the Archer D9 - but 'surprisingly' it didn't get past the TP-Link forum police.

timerrington wrote

Radar, I wrote a long detailed and somewhat scathing post on 17 March about the lack of support for the Archer D9 - but 'surprisingly' it didn't get past the TP-Link forum police.

I was a scathing as I thought I'd get away with.
Clearly no manufacturer is going to support their devices forever and no one expects them to and clearly no device is ever going to 100% correct.
I think what is evident here is that support has been dropped for this device with no official word. Also the last 2 firmware upgrades (the one that is still available and the one that from 2016 that keeps coming and going) were being rushed out and causing more problems than they were solving.
It would be a nice gesture from TPLink to have one final 2017 firmware release for the D9 globally which puts to bed the problems that their user base (the paying public) have kindly let them know about.
Either that or officially retire the product and be done with it.
Of course I'm more than happy to take delivery of a free replacement for my D9 from the latest TPLink range if they are listening(!)
Radar