I seem to have a very similar but even more peculiar issue.
I have 3
routers.
1.
TP-Link TL-WR720N (2.4ghz) router (old router, stopped using because it's max wifi speed is 35-40 mbps)
2.
D-Link DIR-816 (5 ghz Dual Band) (bought it last year to replace TP-Link router
3.
Netgear R6080 (5ghz Dual Band) (bought it yesterday)
Been using D-Link Router since June Last year and it was working properly and I was getting around
90 Mbps on both Lan (desktop) and Wifi (5ghz). (apart from usual excitel connectivity issues).
Started facing intermittent connection issues a few weeks ago and 3 days ago they asked me to reset my modem. Which I did. After the reset, and reconfiguration of Router I only get 9 Mbps download speed and around 14 Mbps upload speed.
I called Excitel customer care and they said that my router is faulty.
I called D-Link customer supoort, and they tried everything from firmware update to firmware flash and still I got 9mbps speed. So they said might be something wrong with the Router and asked me to take to service center. But service center guys refused to accept it as I had misplaced my bill. Okay. Done and dusted.
Ordered a new router yesterday and received it today. It is a NetGear R6080 Dual Band Router. After I set it up, funny thing happened. I'm getting 9 Mbps on this new router as well! I contacted Netgear customer service and they updated the firmware and did resetting and still I'm getting 9Mbps.
What is weird is that the oldest of the 3 Routers, TP Link (2.4Ghz 150Mbps) Router is giving me 90Mbps on Lan (Desktop) and 35-40 Mbps on Wifi.
But newer and more advanced Routers are giving me 9Mbps. I have tried everything, including scratching my head for hours. Still no clue why this is happening.
Please can anyone help?