Lightroom import dialog erscheint immer wieder ungewollt

Please show us a screen shot of what you are seeing on your computer screen.

When I import images I never get any dialog window, box, that asks me that question. And I do not understand what you mean by "when I have imported images that have been imported". You only import images Once. You should never try to import images a second time even if you moved those images outside of the LrC interface.

Images that are already in the LrC Catalog file will show up Greyed Out with no way to place a checkmark on them. And you should never uncheck the option to "Don't Import Suspected Duplicates". Doing that will cause you a lot of trouble down the road.