Xperia Z3 always awake sometimes, even with Stamina, Ultra Stamina, Low Battery modes

Question

Hi to all,
Has anyone every noticed his/her Z3 always awake (and thus bad battery life), even from within Ultra Stamina mode with no running apps?
This happened to me twice now with just over two weeks of using this phone. I haven't been able to take specific steps to replicate this yet, but 2 days in about 16 days means so far over 12% of the days.
Usually, the phone lasts over 24 hours with moderate use. I normally have stamina mode "on", and set to activate at 50% battery level, and then Low Battery mode to activate at 20%. Note also that all the apps I am using have been installed from the first day I've been using the phone. That is, I have not installed any new apps before I noticed this happening, and when I have "normal" battery life it is using the same set of apps.
Here is an outline of what happens:
I notice a much faster than usual power drain, despite being a typical day of usage (i.e. nothing out of the ordinary).
I go to battery usage, and see the history details, and see that "Awake" has been on constantly, including during long screen off times, and all the while with Stamina mode enabled and active.
I then restart the phone. Problem still there, still constantly awake despite screen off and stamina.
Battery dips below 20% and Low Battery mode activates.
Phone keeps on being constantly "awake", despite no usage and now both low battery AND stamina modes on.
Restart the phone. Same problem.
I turn on Ultra Stamina mode. (I did this last time at 17%)
Phone continues to be always awake. Battery quickly drains down to 5% within less than an hour and almost no use, even though Ultra Stamina is supposed to stretch the life for an order of magnitude longer than that.
I shut off the phone to avoid complete discharge. When I return home, I plug it in and wait for a decent charge before turning the phone back on.
After full charge, I take the phone off the charger.
Phone now works normally again, without always being "awake".
I can't figure out what causes this sequence of events to kick off in the first place. I'm trying to play around with things to get it to start doing this, but so far I haven't been successful in deliberately replicating the problem.
Anyone else experience anything like this before?
My android version is 5.0.2, v. 23.1.A.0.726.

Answer 1

Perforn a clean update and report back in 3-5 days
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Alternatives on How to backup Xperias
http://talk.sonymobile.com/thread/36355
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