My lenovo s920 freeze, shut down or reboot randomly?

Sometimes, i put my s920 in my pocket and pressure is giving. The phone may can't on at all, need to take out battery and put back then just can turn it on back.
I hate doing this at outside, my country security not so good and many thieves and robbers.
And one more thing, don't tell me this is software problem, i take to the shop(where i bought my phone)the ppl take my phone for a day and i went back the next day, he said it was software problem and this problem(freeze, shut down or reboot randomly)won't occur again but it still occur.
Additionally, the lenovo community ppl keep telling me software problem, but after i said i take back my phone from shop and the ppl tell me that it was software problem and the problem won't occur again, but the problem is still occur then they all quiet and never reply me already. I need to get my phone good back.So, please help me and don't say it was software problem bcos it was not software problem.

Have you tried replacing the battery? If it is not aa software problem then maybe the battery is dying. If its not the battery than it is internal and you will have to replace the phone.

Try these
Change the battery
Clean install the os (android os)
Still occurs
The problem with mother board
But I'm sure the probkem with os
If not mother board

Have the same problem on a859. Rebooted, restarted and nothing