Instagram has released an update to their App which fixes this issue. Please download the latest version again as soon as possible which should fully resolve the issue with Instagram push notifications.
A number of users have reported issues with Instagram Push notifications. These issues have also been reported by other third parties and looks to be due to an unannounced update on Instagram's end. We are monitoring the situation and looking to reach out to Instagram with regards to any updates that are needed on our end to ensure that Push Notifications prompted through Sendible work correctly.