The page served is a hosting-platform error, not your product
The response claimed success, but the page returned is the error screen your hosting platform shows when an application crashes. Visitors see a platform error instead of your product, and because the status code says everything is fine, uptime monitors that only check status codes will not notice.
document contains "DEPLOYMENT_NOT_FOUND"
How to fix it
This is your application failing at runtime rather than your host failing. Open your platform's function or server logs for the failing invocation — the stack trace there names the cause. Common causes are a missing environment variable in the production environment, a database connection that works locally but not from the deployed region, and a build that succeeded while the runtime import failed. Verify by loading the page and confirming your own content renders.
Referencetech.platform_error_document