I havent had problems with Nikon D3400 until I download the SnapBridge app on my phone and tried to connect the two. That never worked either, and
suddenly after 20 photos good the rest of the hour all photos cant be displayed in the camera nor the NEF file read.
The exiftool doesnt support D3400 so I was wondering what else could I do. I saw the image right after the photo was taken on the screen so thought nothing of it, until....
I think you're talking about the "fix_corrupted_nef" utility. But this won't help you in this case because it only fixes files corrupted by Nikon utilities. Try running "exiftool -validate" on the bad NEF files to see what it says.
- Phil