Damaged Library Problem

One of my peers just ran into this problem of having their library damaged. I haven't run across this before, have any of you?

After opening the library, there is a popup that states "The Library "____" is damaged. The item '(Name of a project)' could not be read.

Once I click "continue", we can keep editing, but the core problem is that it is not saving the projects. Close it the library after working on it for a few hours, and upon reopening it won't save anything. What's the cause of this, and what's the quickest way out? Restoring a backup doesn't seem to solve the problem, though it's possible that the backup isn't going back far enough.

Edit: I went into the Library package, and deleted the project that "could not be read". Then I tried creating a new library, and then copying the main event into that new library. The thinking is that I would just give up on that project by deleting it. However, when I try to copy it, there are still issues with the projects.

We did some checks and the drive is in good health.