iFrame fails to load content from Google Cloud Platform intermittently

I have a web app written in React + Redux for the frontend and Flask for the backend and is hosted using the Google App Engine. The app is installed in my JIRA Software instance using atlassian-connect.js. The iFrame intermittently fails to load the app. This behaviour is also noticed whenever an update is pushed to the app on Google Cloud. Reinstalling the app fixes the issue sometimes. The app runs just fine locally or when accessed via Google App Engine.

Can someone tell me what could be the reason behind this behaviour?