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| p.1 #2 · Photo corruption problems... |
Data errors can occur at random on a hard drive without the hard drive being physically defective - but not often.
More likely the image data has been corrupted during a transfer from one device to another. The cause could be a borderline storage device or card, a borderline cable, interference of some sort during the copy, incompatibility between a specific card and a specific reader, etc.
Check to see if the main image data is intact or not, and separately check to see if the image preview data is intact or not. With an appropriate utility you might be able to extract a usable copy of the built-in preview image.
I use a program called image verifier that applies (and then scraps) a DNG conversion as non-destructive (read-only) test of image data validity. It shows up problem or suspect image files and then I can hunt down previous backups for a better quality image file.
There is almost no practical way of preventing defective images from getting into the automated backup process but you can at least try to find them before they ripple right through the historic backups of backups of backups. You do need to have multiple levels of backups or at the very least multiple discrete backups taken at different times so that the older ones are not influenced by anything that happened on the computer more recently.
In Lr I even created a folder for suspect files and that ensured that I always knew which ones to watch out for. Some of my old archives are in storage and not accessible to me at present but I still know which images I need to find when they are accessible.