Data stored in Backendless stopped being displayed in the app

An iOS app that exists for almost 2 months has stopped to display data stored in Backendless. The problem can be solved by re-installing the app, but we can not force 10k users to re-install our app. How do diagnose and solve this problem? I don’t know from what to start and what may cause such problem.

Create a test project that uses the same API as your app to load the data. Make sure the data is returned from the backend, check for any errors which may be returned instead.