I solved my problem with the ASUS Mainboard. I just needed to update the BIOS and the enable above 4g decoding

did you guys got anything higher than 15.7 Mh/s??
I was playing with my cards to get them over 14Mh/s. i got sapphire rx560 4gb with micron.
I cant remember what exactly i have changes, but i got one (the one i was playing with) to mine with 18.xxx Mh/s. But the machine crashed after 2min.
I restarted it and played with the settings again (lower memory and core) but it didnt help. Still at 18.xxx but crashes after some seconds.
So i let it rest and tried smt else.

Now i am mining with 13.5x stable.
I read someone got the with 15.xx and posted his rom. Gonna check it out later.

I will try to find the rom that got 18.xxx and post it here. Maybe someone can get it stable?

just wanted to share my experience