Why I am getting multiple notifications from the same App on my iPhone?

Now can someone explain why there may be multiple notifications from the same app? Whether it be recent or hours in between I figured notifications from the same app would be stacked but recently I noticed Instagram gave me a notification than 3 hours later another separated one…. Yes other notifications had appeared in between but I always thought that each app notifications would appear stacked on the Home Screen and not completely separate being they are the same app…??

[Re-Titled by Moderator]