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.
I also want to point out that I've seen similar corruption in the past, only in Lightroom. The culprit ended up being hardware, not software. Specifically, the card reader's USB cable. I've actually had two of these cables fail on different readers. On the most recent one, I replaced it with a nicer Micro B to USB C cable, and haven't had an issue.
If nothing else, it lets you get your card back much more quickly, as a file-system copy runs at ~1500MBps, which makes a difference when importing 50-100GB of photos.
I also don't delete the images off the memory card until they've been backed up from the disk to some additional medium.
Generally I'm frustrated with the state of USB. Bad cables are all over the place and I'm inclined to throw cables out if I have the slightest problem with them. My take is that the import process with Lightroom is fast and reliable if I am using good readers and good cables; it is fine importing photos from my Sony a7iv off a CFExpress card but my Sony a7ii has always been problematic and benefits greatly from taking the memory card out and putting it in a dedicated reader, sometimes I use the second slot in the a7iv.