Okay i give up. It realy seems to be a slicer problem.
Youre last post motivated me to overhaul my printer again. My prints are realy nice at the moment.
I already asked the people from prusa forum about this problem and they told me that is a problem with prusaslicer. Some one usesed simplyfy3d and the problem didnt accoured. Than he used prusaslicer with the same file and the problem accourse.
Thanks for youre nice help!