Did you check the drive where the affected files are on for errors?
What happens if you replace a file of the affected ones with the same file from a backup (no LR action, replace the original file with Explorer/Finder), can it be read after that?
Thank you, I did not yet check the drive for errors, I guess I am not sure how to do that. But I can try that.
I did try replacing a few of the affected files with the same files from my backup, and this results in the file working normally, even in develop module. But I am worried it's going to happen again. I will go ahead and check the drive for errors next (can this be done with the Disk Utility?) Thank you.
How to check the drive depends on your OS, which you haven't told us so far. There are OS built-in solutions as well as plenty of additional tools.
The fact that replacing the original files turns out to solve the problems would definitely lead to the conclusion that the drive is due to be replaced as soon as possible.
Thank you. I have been using the Apple El Capitan OS for the past week, but this was happening already with the previous version of OS.
I will be replacing the drive, too. I am pretty sure this wasn't happening before the new drive.