Hello guys ....after many days struggling with this annoying problem and even calling the service center to no avail I found the sure solution to it ...You won't believe me when I say it shortly that it's all because of Viber ...I uninstalled it and restarted the phone and it didn't happen again ....but of course you will say Viber is important and it's a must-have app for any Android phone....Don't worry about it Kakao is much better and it's service is way way better ...I sear this solved the problem for me ....try it yourself and waiting for your response.
