Unable to view Nikon Zf thumbnails when importing NEF Files to Lightroom for iPad

When I import RAW files (NEF format) from the SD card from my Nikon Zf, I cannot see the thumbnails in the import dialog.  All I see is a black box with the letters "NEF." This means I cannot intelligently select which photos to import, as I cannot see the thumbnail preview.

I do not have this problem importing NEF files from my Nikon Z8.  Ricoh GR iii RAW files, in DNG format, also import fine.  With the Z8 and the Ricoh GR iii, I can see the thumbnails.

I have had this problem for months, and it impaired the utility of the Zf while traveling in Vietnam.  I chose to use JPG's (those show up fine in the import thumbnails) but I would have preferred the NEF files.

Any suggestions?  This seems weird, at least to me!

Thanks,

Jim Moyer