Why is Instagram cutting off the captions in my video?
Videos that are longer than 60 seconds need to be posted to IGTV instead of the Instagram Feed. IGTV requires the 9:16 aspect ratio for videos, though.
When you post a video to IGTV, Instagram will automatically crop off the top and bottom of that video to turn it into a square to display on the Instagram feed. If someone clicks through on that video, it will display the entire video, but it will still display as a square video in the feed.
If you want captions to appear in your video in the Instagram feed, you need to move the captions and headline to the center square of the video. This way when Instagram crops off the top and bottom of the video those captions still display in the Instagram feed.
This is a limitation of Instagram.