Hi @SKenduser1,
First of all I want to apologize for a late reply, I've been out of office for a while.
I'm sorry to hear you are experiencing this.
If you have tried what's previously been suggested in this thread I would recommend that you wait until you have received your new SIM-card. A defect or faulty SIM-card can cause the phone to reboot since if your handset loses connection to the SIM.
Have you now received your new SIM? If so, please let me know if there was any change when you started using the new SIM-card. 
Dear Didrik,
Thanks for your reply.
I've already received the new sim.
But the problem still exsist...
The screen would freeze and few seconds later reboots by itself.
Also noticed it would restart itself even without using or touching the phone!
Things I've already tried:
- Factory reset on device itself and using software repair with Xperia Companion, problem still remains after trying out both methods...
- Booting in safe mode, phone still reboots after X minutes...
- I've also tried using the phone without SIM or microSD card insert, but it will still reboot after X minutes... (I'm sure the SIM and microSD is not faulty, as its functioning fine in my Xperia Z5)
In the mean time I’ve received update to the latest software (39.0.A.1.250), but sadly it didn't help 😕
I've contacted Sony Belgium but they couldn't help me because the phone is bought in Hong Kong. 
It seems only Sony Hong Kong can help me... so I've sent it there now.
Very disappointed at Sony Belgium services! 
I'm sorry to hear that @SKenduser1.
The way that you describe what you are experiencing makes it sound related to hardware rather than software. My guess is that you made the right decision in having your phone sent for repairs. I would, in this case, recommend that you wait until the service centre has examined your phone.
As far as I know the warranty isn't global, which might be the reason that you had to send your phone to the market it was purchased from. I would suggest that you contact your Local support in order to get confirmation on this as they will have more information on this subject.
I really hope this works out for you smoothly
Hi Didrik
I hope so too... 
I'll try to update once I have more news from Sony HK on this matter...
Best regards,
SK
@Didrik Thanks for your posts...
I've received update on the repair...
It seems the software got corrupted unknown reason.
They needed to perform a deep reset that only at Sony service center can do.
Regular reset on device and using Xperia companion does only like 80% clean install?
The engineer tested it and was back normal he said… (let’s hope so…) 
I’ve also got noted the device did not pass the pressure test, because one of the plastic edges is not closing properly/minor bended…? 
To get this replaced I need to pay like 55€ and wait 3 weeks for replacement parts from Japan to arrive.
Guarantee does not cover this because the phone is already being used.
I really don’t understand how this could happen, due to the fact I didn’t even have a chance to use this phone properly in the first place and it’s still new…
Grrrr… not happy at all at Sony!!!
The Phone is going to be sent back to me now with just the software repair.
The waterproof thing I don’t really need anyway, so not going to get that fixed.
Let's see how it goes... when receiving back the phone.
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