Your videos are being flagged for copyright issues
Recently Instagram removes videos from its API that contain copyrighted or potentially copyrighted material. This means that a video may show in your feed and work in the Instagram app, but will not show in our plugin’s feed. It is enough that you post to include any songs or parts of movies that are longer than 1 minute in length (though it’s not clear exactly what will flag something to be removed, and it can happen for much shorter snippets of sound).
You can try shortening the video or removing any background music to see if it will display in the feed.
This can even happen when using the included music that can be selected when creating Reels, so if you want to ensure your posts show up in the feed ensure you select music that has a Creative Commons license or that you have produced yourself. You can read more about Instagram and Copyright here.