Share your experience!
Hello there,
A week or so ago I've updated my Xperia Z2 to marshmallow, and although everything went relatively well at the time, yesterday the phone started to lock up when opening some apps. Not a specific one, by the way. I did the soft reset (hold power + volume down) several times to no avail. When I connect it to Xperia Companion to restore, the app crashes when I unplug the phone. Screen is not responding at all to touch. I can start phone by using the method above, but nothing else.
After a few attempts (and a lot of Googling) I've managed to restart the phone on Safe Mode, tested everything, and uploaded a bug report to my Google Drive (although that means nothing to me). I'm afraid to say that, but Marshmallow really stuffed up my phone, and now I've pretty much ran the phone flat and it's there charging, but unresponsive.
Anyone would like to see the report for bedtime stories? Any other suggestions, since phone doesn't respond even to Xperia Companion and resets?

You can use the small yellow button under your SIM flap for resetting your phone.
Did you try performing software repair using Xperia Companion while phone is shut off?
Hey Quester,
Thank you for the reply. Everytime I turned the phone off Xperia Companion would crash when I get to step #5. I've also tried to start while plugged to no avail.
Husband just got home and I've managed to get to factory reset using Safe mode. Phone is restoring while charging, but will get back to you to see how this goes. I have a couple of screenshots from my CSI while on safe mode, see if this makes any sense. Thanks again for your time
(warranty of phone expired on May 30. Lucky me, huh)? 
System UI is a core protected application, I think factory restore is a good choice. And I also suggest that you uninstall then re-install Xperia Companion from your PC.
Keep us updated.
Thanks! Looks like access through safe mode allowed me to restore phone and everything is working fine so far. I'll reinstall Xperia companion as well. Looks like everything is back in place (except for my text messages, the backup didn't work on safe mode - hopefully it will next time). Solved for now. Thank you very much!
Most of the issues can be solved by the user (unless it's a hardware issue) if you have enough patience to try.
Hey, guess what.
Less than a week and the phone played up again. Now it just gets stuck on the restart page and the animation shortly before the home screen loads, restarting on its own.
Tried to restart safe mode, it doesn't let me even do that.
Time for funeral?:smileyskull: