I'm having a very unusual problem with Lightroom 5. I am making digital copies with my DSLR of 21,000 35mm color negatives that image the entire US along I 80. They were made back in 1977. This link will show you examples made from scanned prints some years ago - http://reedestabrook.net/projects/crosssections.php.
I copy the files onto the main storage RAID on my MacPro*. I then import them into Lightroom at their existing location. Nothing particularly remarkable about this until very recently. I've been using this procedure for about a year.
The film segments and therefore each "batch" of imports is about 250 images at 16 megapixels. The original film captures were in 250 exposure rolls made with a Nikon SLR and I am copying these with a DSLR, illuminating the film with a color head aimed upward and a copy camera on a stand aimed downward and using a "Beseler Negatrans" to transport the film across this "stage".
This has work fine for quite some time until recently when during the imports the early files in the import seem to record correctly but later ones don't. The later files are pixilated, sometimes grotesquely. I've checked the files themselves with Bridge and it is not the files problem; it is the import.
Further complicating this is that files imported as long ago as a year with no abnormalities, when opened again in Lightroom after 6 months or more, are displaying the same problem where before there were no such abnormalities.
One bit of info that might be relevant: I had recently upgraded to LR 5.7