[mort96]

Ross Burton on Mastodon suggests that it might be deduplication; when writing sequentially, later files can re-use blocks from earlier files, while that isn't the case as much when writing sequentially. That seems plausible enough to me.

[mort96]

I've concluded that this can't be the reason. It'd only result in an error where the size reported by 'du' is smaller than the apparent size (aka number of bytes reported by 'wc -c') of the file. What we see here is that the size reported by 'du' is almost twice as large as the number of bytes. That can't be the result of dedpulication.

I'll chalk it up to "some APFS weirdness".