If Lightroom shows the images as grayed out while importing, it means they are already present in the catalog.
It could be possible that they are present in other folder and not the one you are looking in.
You should do a test search for one of those images.
Select All Photographs under Catalog panel in Library module > enable text filter > type in the name of one of those images and check if Lightroom shows the result.
If it does, command click on that image > choose Go to Folder in Library and it will show you the folder in which that image is present.
Have to agree with Chetna. The reason they are grey is because LR knows they are already in the catalog you are trying to import to.
Thank you so much. I had inadvertently already imported the missing pics.