[ZenFone 2 Q&A, Help & Troubleshooting] DanielKennethRego:
I've been experiencing a strange system/UI/OS bug for the past couple of months, and I've finally decided to take the time to post about it and see if anyone else encounters this.

TL;DR version: Upon restarting the phone, the Home and Recents keys will not respond with the expected software functions, although haptic feedback still occurs. After opening any app, pressing the Home button doesn't bring up the home screen, repeatedly pressing the Home button will eventually result in a blank, black screen with only a notification bar being displayed (see screenshot), and once this state is reached, there is no way to return to any app or the home screen. Multitasking/recent apps menu doesn't display, and instead of the home screen, a plain black screen with only a notification bar exists. Upon rebooting, the phone returns to the initial state described above - the home screen is displayed immediately upon boot, but the Home and Recents keys do not work as expected, and after leaving the home screen, there is no way to return to it.

Detailed version:

Upon restarting the phone, the Home and Recents capacitative keys do not work as expected. The Back button works as usual. There is haptic feedback when pressed, but the Home key doesn't bring up the home screen again, and the Recents key does not bring up the recent apps multitasking menu. If I leave the home screen by launching an app, for example, there is no way to get back to the home screen again by pressing the Home button.

If the Home button is pressed several times in a row, the active app finally gets minimized but instead of the home screen, a completely blank, black screen is displayed, with no features apart from the notification bar (see attached screenshot). Only the notification shade works, and interacting with the present notifications works only to the extent of interacting with buttons and commands in the notification entries. eg. Toggling WiFi or Bluetooth on and off, or notification drawer controls for apps like Tasker, music players, etc. However, tapping on the notification entries for those apps DOES NOT open the respective app, but returns back to the blank black screen with only the notification shade working. Attempting to open Settings via the 'gear icon' at the top-right of the notification shade doesn't work, long-pressing Quick Settings entries like WiFi or Bluetooth to open their 'advanced configuration' windows doesn't work either. Only simple toggling.

However, Asus apps in the Quick Settings section launch and work normally - Calculator, Flashlight, Bluelight Filter, etc. Pressing Home from one of these apps takes you, again, to the blank black screen with the notification bar.

This is most probably NOT a hardware problem, because haptic feedback is produced upon pressing the key, and also because long-pressing the Recents key produces the expected result (as configured in Settings)- bringing up the active app's menu, and double pressing the Home key also produces the intended effect of toggling One-Handed Mode.

This seems to happen almost every time I restart the device. After 5 - 10 restarts in a row, the device will randomly behave normally, and will stay completely functional until the next restart, and the entire cycle will repeat again.

What I've already tried

I've tried using a different launcher (although this is clearly a system-level bug, not to do with a specific third-party app). No difference.

I've tried rebooting in Safe Mode, which just leaves me with Asus Launcher crashing ('Unfortunately Asus Launcher has stopped') in a loop. I usually use Nova Launcher, but in Safe Mode only pre-installed apps work, so Asus Launcher is active but crashes immediately upon boot, and immediately crashes again in a continuous loop each time I click 'OK'. The phone is unusable because you can't actually do anything before you the app crash dialog pops up again.

Does anyone else experience this, and any ideas as to what's going on? My hunch is that it's a system level UI/OS bug, not a hardware issue.