On June 1st, Instagram changed how apps work. We are no longer able to provide the exact same experience as before, but are working hard on a solution! For now, you can access your notifications through Instagram for Chrome and soon we'll bring back as many old features as possible as well as some awesome new features.
Some of the awesome new features are Grid View for the main feed, tools on instagram.com, and desktop notifications. We hope you'll keep Instagram for Chrome installed until these features are ready!