I know that when you have a task associated with an app and you delete that app then the task is also deleted. I have not tried this to see what happens when you do what you did. But I suspect something similar happens.
So I think that you will need to rebuild the task chain at least from where it broke.
I expect hat you are going to update, change the existing app. If you do so take a copy first, make the changes and do a publish and replace of the existing app. Of course you have to publish the original app first.
By the way. Deleting and replacing with the same name does also loose all bookmarks, personal dashboards,... Only Publish and Replace keeps all these. Same for dashboards within the app!