If it was an HDD, a bad block may be the culprit (these have actual spinning magnetic plates and they do get some areas on the plate that begin to lose magnetic cohesion or the mag-signal deteriorates from moving the drive around near EM sources). IF a flash drive or SSD, you’re looking at some possible format corruption, or even a burnout transistor (the last one is similar to a bad block, but is a physical burnout of a transistor, making it useless, whereas some simple magnetic drop can be re-magged by some software tools that will repeatedly zap the section to rebuild the magnetic properties; the first is more a software type problem, referring to the files that define the drive for the operating system). If you haven’t guessed, I used to do some light IT work for a few offices, mostly freelance repair and recovery.
When They’re finished with the project, have them back it all up, and then attempt to run a check disk in windows, or a volume repair on mac. This will at least tell you something about the drive, and should fix most smaller problems. The larger ones will show up, and you should get an idea of what they are. If this occurs and the repair won’t work, try reformatting the drive and run the repair again. If the drive is still physically functional, it should just pass the testing phase and finish. IF the drive has hardware issues that are more a “time to get a new drive” kind of problem, it will fail the repair again or fail to format.