So Asus official taobao sent a replacement unit back to me. Now just waiting for it to arrive. Will sell it off since I already have a replacement router.

Some timeline for benefit of others.

11/11 bought router during sale. Flashed merlin, installed cooling fans since 1st day. Router positioned on high cabinet with very minimal dust area. (unlike a poster here who thinks everyone puts their router in a sawmill factory  )

13/4 router just died during daytime. No lightning whatsoever, it was a sunny day. No LAN connected except unifi modem.

contacted taobao agent in LYN who bought the router for me to contact Asus China.

23/4 sent router back to China using Poslaju Air Parcel (RM62 + RM15 insurance). Declared parcel as modem. Took 17 days to arrive, quite late since this is the cheapest postage.

10/5 router arrived at Asus China facility.

13/5 Asus China sent new replacement unit to taobao agent warehouse without further question. Problem statement already explained during first communication. Then have to fork out RM44 postage from warehouse to Malaysia.

So total spent for this RMA was RM121.

FYI. RT-AC86U local unit is selling at RM899 at Lazada now. Today only!

FYI. RT-AC86U local unit is selling at RM899 at Lazada now. Today only!

FYI. RT-AC86U local unit is selling at RM899 at Lazada now. Today only!

perhaps ..prepare for RMA caused selling at low price ....

FYI. RT-AC86U local unit is selling at RM899 at Lazada now. Today only!

Local unit has 3 years 1 to 1 exchange warranty by ASUS Malaysia. 

I see more complaints with failure on China RT-AC86U.

If you want to get RT-AC68U from Taobao, might as well get RT-AC66U locally.
.........

Supplied faulty router from China (GDEX no is not traceable, arrived after 11 days) without warranty card. The speed fluctuates too rapidly and extremely unstable. This China unit can’t get support from Asus MY. Seller refused to support warranty claim unless I change my poor review. So unethical

https://shopee.com.my/-Ready-Stock-ASUS-RT-...4761.1359873119

sharing here...less than rm700

not sure if it's legit though haha

Having problem with 2.4Ghz, will disconnect few seconds and reconnect back.

I'm not sure whether its my phone problem or router

Btw, I'm using iPhone.

Hopefully not router problem 

You could try changing some of the wireless options in the 'Wireless - Professional' tab e.g. disable  WMM APSD. I don't have an AC86U, my main router is an AC66U but I expect the options are similar. Usually it's a case of changing one of the options and trying for a while.

There's a lot of good information at  https://www.snbforums.com/forums/asus-wireless.37/

I just received one ac68u from China yesterday. The seller said it's a US unit. It's been working great so far, good range and responsiveness, blows the 850L out of the water no doubt.

But I'm having some issue with the 5GHz channel. The problem is :
1) the available channel is only up to 140 ( I know there are still some channels available beyond that).
2) my pce-ac68 (local unit) can't detect the 5GHz band when channels set above 48. (means 100 and above it just can't detect at all).

Other than that, it works fine with my other devices like my iPhone and MBP. Can detect the 5GHz band regardless what channel I choose.

So far I've tried rolling back the driver on the pce-ac68 to older versions, both EU specific and non-EU versions. Doesn't help at all.

The router is on latest Asus firmware Version 3.0.0.4.384.45717.

Can anyone shine a light on this?

*I don't want to post this in the official Asus networking thread as my router is not bought locally.