The "first comment" feature is something that we offer customers to let them have a cleaner feed by putting their hashtags into a comment rather than the caption (for more, see here).
Despite being launched in May 2014, this feature is still in beta - and is still labelled as such in Schedugram. The reason we have kept it as a beta feature is because of how we have to post the comment: obviously, we need to post the image itself first. After posting the image (and detecting that it was successfully posted) we can go and add the comment to it. That means that if something goes wrong, the image will be uploaded without the comment – if it was the caption that failed, the image wouldn't go up and we would retry the post automatically, so captions are not affected in the same way.
Sometimes first comments might not appear. This can unfortunately be for a number of reasons (including Instagram simply being buggy in the process), but some of the common causes we have experienced are below.
Not having a verified email or phone number
Sometimes Instagram will insert a little message box above your feed about verifying the email address or phone number on the account ("Confirm this email" is the button). You should login to Instagram on your phone and check the profile page to see if there is a message – this can stop us being able to "see" the recently uploaded image.
Consistently posting a high number of hashtags
While Instagram limits you to 30 per post, that doesn't mean that you should post 30 all the time. Fewer, more relevant hashtags will always be better than just any hashtag, and Instagram has a range of spam and other filters to make sure that accounts aren't abusing their service. We generally see higher error rates for accounts consistently posting high (>20) hashtags in comments or captions.
Posting long captions or comments
This is similar to (2), but we see higher error rates (in almost every type of error) when you are posting long captions and/or comments frequently. Not sure what the cause is (the Instagram app "crashes" sometimes when we're writing the comment for example), but reducing the length (+/- number of hashtags) of your content is likely to reduce the errors associated with it.