These are probably corrupted files. The corruption comes from a hardware malfunctin somewhere, it could be the camera card or the card reader/USB cable, the computer's hard disk or the computer's memory. Please try re-importing the photos using different hardware, and if possible using an entirely different computer to see if you can isolate the problem.
Given that it seems to happen with all the files, I would first look to see if the monitor profile has become corrupted. LR is very sensitive to that.
Otherwise, the image files are corrupted. This is usually a hardware failure somewhere in the chain: camera, memory card, card reader, USB cable, hard drive, computer memory. (USB cable and memory card are the most common causes.)
I'll look into an alternate way of importing these files through.
Thank you for your input.
I'll check on the possible "failures" that you've mentioned. Thank you