Old photos on my phone started changing, and I can’t explain how

This is going to sound made up, but I noticed something weird with my old photos. There’s a picture from a birthday a few years ago that I clearly remember. There were five of us in it. I opened it recently, and now there are only four. I thought maybe I was remembering it wrong, but a friend confirmed someone else was there that day. So I checked other photos from that time. Same thing. The same person is just… not there anymore. No cropping, no edits. It just looks like they were never part of those moments. I tried looking for messages or tags with them. Nothing. It’s like all records of them are slowly disappearing. Even trying to remember specific conversations with them is getting harder. I don’t know how to explain that part.