Z3+ freezes completely

[Pacoura]

HI guys, 

I was just watching a video on YouTube when the device freezed, stoped responding to touch,even the on screen buttons and power button are not responding,then after at least a minute the phone restarted with the notification led flashing red,this is the second time to have this problem 

Any clue on what should I do or where could be the problem? 

Sorry for my bad English it's not my native.

[Muxis]

I had the same problem with my phone. After doing all the factory resets it did not help. So I gave my phone to warranty service and they needed to replace the motherboard to fix the problem. Now the problem is fixed for me so I think it was motherboard hardware problem.