Claudia is finding that half of her photos have disappeared in Apple Photos. She's taken her computer into the Apple store and talked to a genius but they have no answer, except that she has a second library. But the photos aren't there either. Leo says that the second library is the old iPhotos library. But that doesn't answer why her photos have vanished. They've also disappeared from her backup. Apple wants to wipe her drive and start over. Leo says it's common for tech support to want to wipe and go back to the original install. But the problem is, she'll lose her data. It certainly doesn't help Claudia and it doesn't address the fundamental issue that her photos are disappearing.
Leo says that it could be one of three things. It could be user error, a random software glitch, or hard drive issues. Leo says hard drives can and do fail, and will fail more often the older they get. If her hard drive is slowing down, that's a sign the hard drive is getting ready to give up the ghost. Spontaneous random deletion and spontaneous errors are indicative of a failing hard drive.
Another possibility is Apple's cloud services are the culprit. Claudia is relying on iCloud to back up her photos. Leo advises logging into iCloud from her desktop to see if the photos are still there. She should also check in the recently deleted album. Apple really isn't as good at cloud services as Google, Amazon or others. It could also likely be the most obvious culprit here. That's why Leo advises backing up to Google Photos, Flickr, or some other third party photo backup site. Claudia should also periodically backup her photo library to an external hard drive. Adopt a 3-2-1 backup strategy. Three different copies, on two different media, one being off site. Redundancy is key.