Fix Failing Data Retrieval API

My production web application has a single Data Retrieval endpoint that suddenly stopped behaving. The route had been stable for months, but today every call returns an error instead of the expected JSON payload. I haven’t changed any client-side code, so the issue is almost certainly on the backend (possible regression, mis-configured route, or database hiccup).

Here’s what I need:

• Pinpoint the root cause of the failure (routing, controller logic, database query, third-party service, etc.).
• Implement the fix and push the change to our repo.
• Verify that the endpoint once again returns the correct data structure through Postman or cURL, and that no other routes are affected.
• Hand me a concise summary of what broke and how you resolved it so I can document the incident.

Stack specifics: REST over HTTPS, JSON responses, and a standard MVC server (Node/Express or similar). You’re free to spin up debugging tools, check server logs, and run unit or integration tests—whatever gets us back to green status quickly.

Acceptance criteria: a successful 200 OK response with the full data set, unit/integration tests passing, and zero new errors in the log after deployment.