If every other block works and one app still opens, check the app itself before rebuilding everything.
Make sure it is in a list. Open the Blocks tab and check under Your Apps. Having an app installed does not mean it is selected.
Add it individually. Apple's categories can be surprising. An app you think is Social may sit somewhere else, so select the app by name.
Block the website separately. Blocking the Instagram app does not also block instagram.com in Safari.
Check where the content opens. A video playing inside Messages is not the original app launching, so the app block cannot catch it.
Apple system apps such as Phone, Messages, Settings, Camera, Clock, and Maps cannot be blocked by third-party apps.
Still slipping through? Email help@downloadaura.app with the app name, your iPhone model, and your iOS version.