Usually one sees this, when LR believes the images are already imported. You are certain that your Catalog does not already include them? On my PC, when I hover over one of these greyed-out images, I get a tooltip which (among other things) explains that "this photo has already been imported". Also if you change the selector at the top of the Import dialog grid from "all photos" to "new photos", if the thumbnail grid then becomes empty, that is your explanation. LR doesn't think these are new images.
I believe that the "don't import suspected duplicates" option - which is turned on by default - will also reject images that appear to be mere extra renames of the same original camera file - due to showing the same original capture file name in the EXIF metadata.
But in order for "don't import suspected duplicates" to activate, there have to be images present which these new ones would be duplicates of. So I would advise first checking for any LR filters, or other selective viewing that might be currently stopping you from seeing these if they are within LR.
Repeatedly importing files is likely not the answer; once should be enough AFAICT.