Apple has removed the Like Patrol app at the request of Instagram. With the app, users of Instagram could be monitored and that is why Like Patrol is known as an app for stalkers.
With the Like Patrol app, users can see exactly which messages a specific Instagram user gives a heart to and to what he responds. The app thereby maps the activity of the user in detail and can also give notifications as soon as a user being watched is doing something on Instagram.
Instagram does not want its users to be spied this way and has therefore compelled Apple to take the app offline. Apple subsequently removed the app from the App Store.
Initially, Instagram itself had a tab that shows the activity of the people you follow. This tab was soon known as a handy feature for stalkers. That is why Instagram decided to remove the tab from the app.