To troubleshoot the Instagram push notifications issue further, I would recommend following in this exact order, the below steps to re-sync the Notifications:
1) Turn off Notifications for the Instagram account in the Hootsuite App:
iOS - https://help.hootsuite.com/hc/en-us/articles/204596300-Notifications
2) Clear Message Memory/Reset App Data
3) Sign out of the Hootsuite App and Sign back in
4) Please turn the Notifications back on for the Instagram account
5) Schedule a test post, and check in the app for the notification, by clicking on the bell icon.
Please feel free to reach out if the issue persists and we will be happy to further assist you with this.
Kritika | Customer Advocate