Got it - thanks. That actually wasn’t delivered because of the ‘language=en’ parameter in your request. That only allows Tweets where the text in that specific Tweet is able to be classified as English (as opposed to the user’s profile or something else). There wasn’t anything that could be recognized confidently as English in this one, which is why it wasn’t classified, and didn’t get delivered.
If missing Tweets is a concern, keep in mind that there will never be 100% language classification coverage or accuracy, so you would always expect to miss a few if you filter on it.
Hope that helps!