I have been posting one post after another using Sharing button, type Instagram/story and post right now. Eventually the post is not going in order that was published.
If you are rapidly scheduling multiple posts one after the other, Instagram’s algorithm may process them out of order. Try leaving a little more time between posts, ensuring each one is successfully posted before proceeding to the next. You can also try logging out of both Adobe Express and Instagram, then reconnect the accounts to ensure there aren’t any sync issues between the two platforms.