I bought the AC58U 2 mths back from the IT Fair at Mid-Valley to replace my old AC12N. Speed was much faster about 30% more on 2.4Ghz and 50% higher on 5Ghz on my Unifi 50Mbp plan, notwithstanding the frequent drops in my internet connection especially on 5Ghz channel.
Last week out of sudden the AC58U stopped working. The unit is still powered but no internet connection on both 2.4Ghz and 5Ghz.
The WAN LED light is off. Still can see the WIFI connection on my phone but the small "lock" icon (think this indicates password protection to the WIFI connection) is no longer there.
What could be the issue?

Thanks for the heads-up. Will try your suggestions.

I am using AC58U. Speeds especially the 5Ghz is fantastic almost double when compared to RT-12N.

Had issue 1 month after purchase - it suddenly stopped working and have to update firmware to get it back to work (so for user that have zero knowledge on how to access to the router for maintenance will be an issue).

Anyway still dealing with 1 issue - frequent drop of wifi signals - 3 or 4 times within 4 hrs where your wifi connections dont even appear on the list of wifi available for connection - they don't last long just around 10 - 20 seconds and the wifi connection will resumed automatically but the interruptions could sometimes be irritating especially if you are in the mid of using the internet connections for works.

Tried to set the bandwidth fixed at 40 for my 2Ghz (instead of 20/40) and 80 for my 5Ghz (instead of 20/40/80) the problem still persist but improved in the sense instead of 3 or 4 times now may be 2 - 3 times every 4 -5 hrs.

Hope any Asus technical support in this discussion forum can advise a solution.

Mine AC58U not only wifi signal intermittently drop but totally no internet connection including LAN connection from the router to my TV Box.
All lights off except for the power light.
It happen whenever there is new device connected or during internet high usage.
Tried to fix the bandwidth to 40 (instead of 20/40/60) for the 2Ghz and 80 (instead of 40/60/80) for the 5Ghz its helped a little less frequent drop but nevertheless still dropping.
Called Asus technical support wifi signal drop is not uncommon but LAN connection stop at the same time is unusual. Got to send to service center for checkup. So troublesome service centre only open Mon - Fri 9am to 6pm.
Anyone here can help to suggest a solution without me having to waste time sending the unit to service centre?

I have updated the firmware.

Hi AsusMy,

Kindly elaborate on what you mean by "set the channel for the WIFI". I am not so tech savvy. Thanks.
Yes all connected devices (phone, PC, laptop, tablets) will experienced WIFI disconnection during the drops including LAN connection from the router to my TV Box. Basically all lights on the router are off except for the power light.
I have observed it normally occurs whenever there is a new connection by a previously connected device or wherever there is an increase in internet usage.
Please advise a solution. Thanks.