A much more effective tool for tracking unfollowers is using a third-party app.  

There are a lot of apps which promise to help you find people who have unfollowed you, but we recommend one app in particular, both because we have confirmed it works as advertised, and because it's available for both iPhone and Android. 

If you want to give it a try, install FollowMeter for iPhone or FollowMeter for Android. The app is free with in-app purchases, but you don't need to pay for the ability to track your unfollowers. 

To use the app, you need to give it permission to access your Instagram account. Once you log in and give permission, the app will automatically track a number of metrics about your account, including new followers and unfollowers. 

To get more details, tap any of the entries in the dashboard to see a list of users. Tap "Unfollowers," for example, to see the specific user accounts that have unfollowed you.