After some researches, I discover that this is a knowned problem and a fatal issue for all Rog 5/5s/Ultimate. I went to exactly the same issue this morning too and I've tried everything.
Problem is hardware-related, the motherboard has some issues since the release of the phone, knowed by Asus but they don't take repairs outside warranty. And since the problem is the motherboard, i'm sad to announce to you that your phone is doomed and it's only matter of time before he will die. Even if you replace the motherboard, the issue will stand. Mine is outside warranty, so I don't wanna replace the motherboard. Takes time and money to just push back the issue for later.
Also sorry for the bad english, I'm french. Bye dude.
