It's most likely bitrot or clone degradation.
I've been using hashing and checksums for years now to protect against this.
I'd say 1 in 10 file transfers ends up in a mutated file. Using software like fastcopy or teracopy or robocopy, you can see for yourself with the checksums.
We are being bombarded at all times by particles that wreak havoc. Unless you actively protect against this, nothing is safe.
Bad memory will also cause bad data. I also recommend checking your ram. You can download a little iso file and boot it, or windows now has a built in memory check tool. Most Linux live disks have memory checker option at boot.
MD5: 54b3281e98f635f67f585a25ab884158