Whatsapp Freezes and causes phone to restart

Hello everyone,
my phone is Lenovo Vibe Shot Z90a40, Android version 6.0.1, WhatsApp Messenger Version 2.18.361
i also have Malwarebytes Premium which did not detect anything.

i've been experiencing a very faustrating freezes and system restart over the last month, it happens AT LEAST once a day, sometimes 2 to 3 times a day depends on how frequent i use whatsApp, i updated the app several times during that period of time so i had the same issue with different app versions
WhatsApp freeze while i'm using it ( opening a chat room) then it causes the phone to automatically restarts.

i used the following methods nothing helped:
1- force stop
2- cleared catch, then force stop
3- updated the app
4- uninstall and install the app, it was a work around for only a week or so then it started freezing again
5- deleted all the sent media files

NOTHING seems to work and it's divring me mad now! 
PLEASE HELP!