stop importing duplicates?

how stop lr cc importing duplicates, though have "do not import suspected duplicates" checked. i'm new lr, converting aperture. i'm using mbp 2 external hds, while on vacation in europe. importing sd card, 1 hd lr photos, other lr backup during import. each day import 100 200 photos, , each day, lr import images on sd card including imported photos (i not erase images sd card use them additional backup). 1 other issue standard "shift" command not function. can not uncheck photos, select new photos day. use "copy dng" import leica dng image , jpeg image. appreciate help.

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