So dissapointing that nobody cares to resolve these problems.
I have the same problem with my rx580.
So my only sollution I've found that helps for me is every time my card won't go past 300mhz (some days I doesn't have problems, most of the days it does) is that I have to go to safe mode, delete my graphic drivers using DDU and reinstalling them.
Then I can game. It is a pain every time but it works.