thanks for your reply Chris
But Iīm not sure if we are talking about the same issue
only for clearness: I double click a folder in Finder and move the window to the second monitor. Then I close the window and re-open it. Instead it opens exactly on the last position (on the second monitor) it opens on the first monitor.
Before upgrading to Sierra I never had such an issue. I started the mac in Safe-Mode (disabling any extensions), but this issue remains.
I created a new user-account and there this issue doesn'tīt occur ... strange.
I didnīt install sierra from the ground up (clean install) - instead I upgraded from Mavericks, maybe thereīs something left from the older system that causes it