I contacted Asrock support.

They say for some HackFlags solution works on Windows Installations (1709).
But it didnt work for me.

The solution for me was windows 10 (1703), the version before creators update.
My 4 cards (Gtx 1070s) are working with this Windows version, when i update to 1709 only 3 cards are working. So i dont update for now.

The support said its a problem which occur on Windows 10 (1709) versions. So microsoft needs to fix this in a coming update.

Hope it helps, cioa.