Not sure if my inference is correct, but from what I read in the original post, the image files from the SD card were manually deleted from the SD card after download. If they were deleted by using the computer in some way, say by moving the individual files to the Trash, or through a 'delete after copy/download' command, etc., that is very likely the source of the problem.
In my past experience with digital cameras and storage card devices of all sorts, any method of deletion besides the reformatting of the card in the camera, (in this case, the drone and DJI app), can cause the card to corrupt or even fail.
Hopefully reformatting the card in the DJI app will resolve the issue.
And if I misread the post and am completely wrong, my apologies in advance!
