More than one application in the repository
A project may contain an old prototype and a newer implementation with different entry points. The presence of a feature in one directory does not show that the delivered app uses it. Start with package scripts, imports and build configuration, then trace the user journey through the version those commands actually start.
The app works in preview but fails after deployment
A local proxy can make an API request work in the browser while a packaged application has no usable endpoint. Configuration needs to be checked where it is consumed and where the release build receives it. Supplying a secret to a browser bundle is not a safe substitute for a missing server-side boundary.
Errors are disguised as success
A fallback paragraph, a success animation or an optimistic state update can hide a failed request. The user-facing message must describe what actually happened. A repair should preserve useful input, distinguish retryable failures and verify stored state where persistence is part of the promise, rather than simply remove the visible error.