Photos does a lot of extra work on import (merging RAW+JPEG pairs, generating previews, database indexing, optional deletion), so my guess is a concurrency bug where a buffer gets reused or a file handle is closed before the copy finishes.
Rare, nondeterministic corruption fits the profile.
What's the point of it? It is well known in the industry they ignore bugreports.
Also, this bug doesn't affect the majority of users, so it won't ever be fixed.
I'll tell you a secret though that kind of pisses me off. If you have shipped with a bug, that automatically lowers the perceived priority as well. You know, as opposed to introducing a new bug in a new release. "We've already lived with that old bug…" seems to be the mind set. Oh well.
To be sure though, if you saw the number of bugs that queue up for a popular app like Photos, you'd know that fixing all of them is not going to be possible — some kind of system of prioritization is required.
This mentality is all over BigTech: This bug didn't block release X-1, why should it block release X? So, it inevitably just sits in the backlog forever. If your releases are 90 days apart, any bug found has an average of 45 days to be fixed, or it ends up on the "we lived with it last time" list.
“This bug didn't block release X-1, why should it block release X?” Is actually a pretty strong argument and tough, but not impossible, to counter.
And the bug backlog only gets longer with time. It’s the price of greatly increased software complexity.