R7000 slow upload over wifi (android)

Hi

I recently switched my router to the R7000 connected to VDSL line via a Netgear DM200 modem (PPPoE). This all works just fine for most devices connected.

However, for some strange reason the upload speed over wifi for some devices are really bad.

- An iPhone and an iPad works just fine

- All computers running Windows works perfectly fine both wired and wireless

- All android devices fail. Download speed is fine but upload measures at 0.0 (compared to 2Mbps for everything else). Tested this on 2 samsung tablets, a kindle fire, a motorola phone and a sony phone. They're all the same and they all struggle to load certain sites or upload things. The only thing they have in common is that they all run Android in some form. This happens on both 2.4 and 5 Ghz (don't have any wired Android devices).

I've updated to the latest firmware (1.0.7.2) and did a factory reset afterwards, but that didn't help. In discussions for some other routers a few people suggested putting a switch between the modem and router, so I tried that as well without any luck. I even tried downgrading the firmware to some earlier version but that didn't make any difference.

If I plugin my old router (a TP-Link, still via the DM200 modem) everything is back to normal and works perfectly. My old router doesn't support AC or 5GHz wifi though so I would like to get the new one working.

That it only seems to affect Android devices feels really bizarre. I could understand if all wifi struggled, but laptops and apple devices works just fine.

I still have time left on the 90 days free support but I figured I try here first.

Any ideas? Something else I should try?

Thanks