Xperia Z5 (non-premium)
Just thought I should share this fright that I had earlier today.
I had a busy morning, going to Giant IMM, then to Mustafa Centre. So my phone was almost drained from the morning navigation usage and shopping list checking.
I used a Xiaomi Portable charger to juice it up while I took the train to Jurong Point. When I got to my lunch place, I couldn't get the screen on by pushing on the power key. I thought the phone was dead, so I plugged in the charger. That was when it showed the home lock screen before the fingerprint-unlocking. Everything was still working fine, (the fingerprint reader) just that the power key is unresponsive. Therefore I couldn't turn the screen on/off by using the power key. I had to resort to using the camera key instead.
Reluctantly, I went home to backup my data. (Sony likes to data wipe your phone during servicing) I forgot the phone will reset if you pull out the sim/sd card tray, so it did. When it turned back on, the power key is working again.
That's the situation up to now.
tl;dr = power key was unresponsive but works again after forcefully reset by removing sim/sd tray
I hope it was just a rare hiccup