I know. It never happened to my phone before either. I like Zenfone 6 so much - when my camera is on, and wants to point at me, it has to make a sound, and motion, unless the phone is upside down, of course. That's really cool. On the phones with static cameras - you just never really know, for example...
I don't think I'll ever find out what caused it singlehandedly.. Mainly because the camera doesn't log accesses, and requests, only errors. Wait... What if an error actually happened in that moment? Where can I find the error logs on Android?
Okay I found it, I need to use logcat either via adb, or via an app. I looked into it, and all logs are empty, apart from the stuff that only happened maximum 2 minutes ago.
The app logcat can let you log actually any desired app. So, at this point it's the only thing I can do - use the logcat to log the com.asus.camera app while trying to avoid using it completely, and see what's gonna happen in the future. The logcat can be manually configured to log everything that's happening to the camera, not only errors. That's what I did. Now I'll just not use the camera at all, and see, maybe I'll get lucky.
Thank you guys! If I find anything I promise, I'll write about it here!