Ohai. Sorry to intrude on your scraping, but there's something important we thought we should let you know.
Recently, we learned of a bug where users were getting emails with only about 25 comments, even when their post had hundreds more. We've done an investigation and found that this is a bug on Instagram's end.
You can verify if this bug is affecting your post pretty easily, all you have to do is check out the post via Instagram on the web. If you see all the comments there, you should be good to go. However, if your post says it has hundreds of comments, but there's no plus (+) button for you to view them all on the web, then we won't be able to scrape it either.
We apologize for the inconvenience, and are trying our best to find a workaround. Thank you for your patience with us.