Phone suddenly locks screen and does not allow to unlock

[Android Central Question]

Hi,
Sony Xperia Z5 Premium Dual (E6833), with the latest official Android (7.1.1).

The issue:
For quite a while now and while using the phone (e.g. Google Maps, browsing or listening/watching media, social/IM or anything else), it would suddenly lock the and switch off the screen with a specific short chime sound played. What is shown on the screen is the clock and some buttons at the bottom of the screen (for example, the camera), but notifications are not displayed, which otherwise, are. It gets into a loop because that chime gets played every few other seconds or minutes until something happens and the phone recovers.
But until then, it would not let me unlock and back in the phone for a long time afterwards (could be up to hours...), no matter how and what I try to get back in: fingerprint sensor (the sensor itself detects my fingerprint through short vibrations, but nothing happens, as in, the PIN unlock screen does not show up, which otherwise does.
I also try swiping up to get the PIN board up, but to no avail. After a few seconds, screen switches off.
I can switch it back on with the on/off button or double-tapping the screen, but as above, it would not bring up the PIN unlock screen, no matter what I try.
Interestingly, I can bring up the camera and take photos, but I cannot get past the camera and back in the phone.
The only thing I can do to speed up recovery is to long press the power on button to bring up the phone restart screen and reboot. But if I do that, I lose non-sticky notifications every time so it is a PITA for me.

One thing I noticed as relations is that this issue sometimes kicks in when I update apps in Google Play. Not always, but sometimes. I have got auto-update off, even dug deep and disabled auto-updates in the Facebook apps (Facebook Lite, Instagram, Messenger Lite) as much as I could.

Any ideas around how I could solve this issue?

It has become very frustrating and it has also started posing huge danger while driving, when this kicks in while I rely on GPS routing... many times I had to go wrong ways because this issue came up.

 

[methodman89]

Have you tried clearing the cache partition and rebooting? If persistent still, enter safe mode to rule out 3rd party app. If still persists after, time for a repair shop or new phone.

 

[BonanzaGroove]

I have not gone to clear the cache partition manually, yet. I think there was a firmware update which must have done that, but nothing has changed. This must be a software issue which needs proper troubleshooting, which I am really looking to. achieve. I can do whatever repair shops can also do - I especially do not want to reset to factory settings. What debugging can I use to try and find the root cause of this issue?

 

[methodman89]

See my answer above. That is the algorithm. A firmware update does not do it.

 

[BonanzaGroove]

Thanks, mate.
I have followed the simple steps in the following video to clear cache on my Z5 Premium Dual - even though the video is about Z1, Z2 and Z3 (but it mentions "Z series" in the video):
https://www.youtube.com/watch?v=rQCE76-twIM
It is actually much easier than I thought on the Xperias - it is simply pressing the volume up and power buttons simultaneously, until you feel three short vibrations and the phone shuts down. I hope it did clear the cache.
I will be monitoring the situation and report back here in case of still issues. If the issues is not coming back within at least 30 days, I will consider the issue resolved.

 

[BonanzaGroove]

Unfortunately, the issue is not gone. It has occurred twice since my reply above... Are there any other ideas on how I could troubleshoot this? Thank you.

 

[BonanzaGroove]

This is happening also while in Safe mode, unfortunately. The last option you gave, @methodman89 (repair shop or new phone) I would not like to pursue. There has to be ways to debug this locally, on my own. For example, how can I check the system logs, linux dmesg output? This is not a rooted phone, yet - but I would be willing to consider for the sake of debugging. Thanks.

 

[methodman89]

This is happening also while in Safe mode, unfortunately. The last option you gave, @methodman89 (repair shop or new phone) I would not like to pursue. There has to be ways to debug this locally, on my own. For example, how can I check the system logs, linux dmesg output? This is not a rooted phone, yet - but I would be willing to consider for the sake of debugging. Thanks.

Unless you have some app that closes active processes on a timer, safe mode should have resolved it. Since not, the issue is probably related to hardware or a bad processor. Good luck.