What exact version of Lightroom? What operating system? Did this just started happening? Have you been able to import previously? Are there any error messages? What are your import settings? Are you connecting the camera with a cable, or are you using a card reader? Are you using the Copy or the Add Option? The more details you can provide about the problem you are having, the better.
Lightroom version 7.2, macOS X 10.13.3, this just started happening, I have been able to import previously, I apply auto tone settings, I only use a card reader, I use the Add option
I only use a card reader, I use the Add option
If both these options are correct- This will not work.!
Lightroom, by default, will not make a catalog reference to photos on a camera card (either in the camera or in a card reader) as this is not considered a permanent storage location for downloading the photos.
By using the "Add" option you are asking Lightroom to leave them ON THE CAMERA CARD, so 'No Go'.
You must select "Copy" so as to place the photos on a Hard-drive, and LR will construct previews in the library catalog.