LG G2 proximity sensor

I found a big issue in my LG G2 proximity sensor. During a phone call the screen doesn't turn off and the automatic screen lightness doesn't work. This problems happened many times a day. I also tried to do an hard reset but I got the same issue just after the reset reboot (without any app). Sometimes also the gravity sensor holds (screen doesn't turn), but this not so often as proximity sensor problem. I installed a sensor test app and this app doesn't work too (sometimes got data sometimes not). What can it be? Firstly I thought about an software problem, after the hard reset I thought an hardware problem, but it is very strange all this trouble on a 2month old phone. These problems started 2 weeks ago. Is there in android a system log or something like this?