Incomplete import

Using desktop version 11.4.1 in Windows 10.   Attempting import some times takes three trys to intiate.  Then the import is likely to be incomplete and include nil value imagwes.  I now have hundres of nil value images in my catalog that I can't delete.  This issue results when I try importing directly from a memory card.  If I download memory card to a folder in C drive and then transfer to LR seems to work better, but still end up with nil values that appear scattered throughout the uploaded images.  Help!