I'm guessing the more common error, which I've definitely hit years ago, is not knowing that Promise.all returns immediately if any of the included promises reject.
Correct. It was millions of lines of code in a huge code base at a giant enterprise company with 100s of engineers. Somewhere buried in there there was a Promise.all that someone assumed would finish ALL of the promises, and didn't account for the fact that it bails on the first error.