So last week I had the exact same issue. My router was working fine as far as I knew. I just wanted to log into its GUI to change a client schedule setting... It kept saying "wrong password".
I tried a hard reboot. Same problem.
Since I had a saved config file I decided to hard reset the router. Once reset I loaded my config. Everything seemed ok except no wifi. I thought I had toggled the radio button by accident. I had not.
I contacted Asus support. I sent them my log file, my config file, the picture of back panel with the router info etc... The whole song and dance.
They asked me to do another reset using their app and going into rescue mode to refresh the firmware. It didn't work.
They sent me an RMA form to send the unit in for repair. I am out of warranty and also without wifi so the down time was going to be a pain.
Long story short,
@CrashXRu was able to bring my router back to life from across the globe. I don't know how he did it but he did and I am extremely grateful. In mere minutes my AX86U was fully functional again.
I am hoping that Asus will eventually provide a fix that will not require us to send the unit in. I did my part to let them know what was wrong by repeating what
@CrashXRu and
@ColinTaylor were saying on here.
FYI: I had AiCloud and DDNS activated when this happened. They are no longer activated. I don't want to risk it.