Reduce the impact of flats?

@sternefueralle There is no way to influence the way the flats are applied to the lights in APP. I am afraid that if you get such artifacts after applying the flats, that the flats are open for improvement. So you may want to review the way you take the flats in order to get rid of this effect.

@wvreeven Thank you for your answer. I worked it out and found an improvement, that helps me with my flats...sorra, it's my fault. CU

@sternefueralle Out of sheer curiosity, what was it?

I made new flats with an exposure time around 4.6 secs and added dark flats for the first time. Now the master flat is more equal. Not so intense... this works. 

@sternefueralle Yes, creating proper flats and using dark flats or bias frames to calibrate them is the preferred way. In my experience dark flats work better with modern CMOS cameras. Glad to read that you sorted out this issue.

It is strange, that this occurred suddenly. The correction frames I usually used worked very fine. But suddenly, I can not really say when, it behaved strange, as I showed. So I was confused and did bout know where the problem comes from, or better, how to solve... happy to have solved another problem in astrophotography...