Yes I encountered this after 11 days uptime. A manual reboot was the cure for me. Even the app failed to login.I installed (mainly due to vulnerability fixes) the firmware Version 126.96.36.199.386_51255-g486ded6 via admin UI.
After the installation, the router is still operational, but I cannot access any more the admin-UI.
What I tried (chrome + Firefox + both with incognito and w/o incognito):
http://192.168.1.1 => fail
https://192.168.1.1 => fail
https://192.168.1.1:443 => AI Cloud login ok
https://192.168.1.1:8443 => fail
http://router.asus.com => fail (ping gives correct 192.168.1.1)
https://router.asus.com => AI Cloud login ok
https://router.asus.com:8443 => fail
http://www.asusouter.com => fail (ping gives correct 192.168.1.1)
https://www.asusouter.com => fail
https://www.asusouter.com:8443 => fail
Installed "Device Discovery" app, and router is listed with 192.168.1.1.
Now no further ideas how to get the UI working again.
Did someone else encountered the same issue after this firmware update?